Process for producing a transglutaminase derived from streptomyces
FIELD OF THE INVENTION 
     The present invention relates to a process for producing a transglutaminase derived from the genus Streptomyces, and more precisely, to a process for producing a transglutaminase which comprises culturing a microorganism belonging to the genus Streptomyces, which is capable of producing a transglutaminase and harvesting the transglutaminase from the culture obtained. 
     BACKGROUND OF THE INVENTION 
     Transglutaminases are enzymes which catalyze an acyl transfer reaction of a γ-carboxyamide group of a glutamine residue in a peptide or protein chain. 
     The transglutaminases form intramolecular or intermolecular ε-(γ-Glu)-Lys cross-linking wherein the ε-amino group of the lysine residue in the protein serves as the acyl receptor. When water functions as the acyl receptor, the transglutaminases catalyze deamination of glutamine residues to form glutamic acid residues. 
     The protein gelation products obtained utilizing the transglutaminases according to the present invention are used as yoghurt, jelly, cheese, gel cosmetics, etc., including conventional gel foodstuffs and gel cosmetics. 
     In the animal-derived transglutaminase, there are hitherto known, the transglutaminases which are widely distributed in, for example, liver of the guinea pig (Connellan, et al., Journal of Biological Chemistry, Vol. 246, No. 4, pages 1093-1098 (1971)) and mammal organs and blood (Folk et al., Advances in Enzymology, Vol. 38, pages 109-191 (1973) and Folk et al., Advances in Protein Chemistry, Vol. 31, page 1-133 (1977)) and characteristics of the enzymes have been investigated. 
     However, application of the animal-derived transglutaminase to industry, particularly, the process for producing protein gelation products involves defects as described below. 
     It is difficult to obtain animal-derived transglutaminases at low cost and in large quantities. Also, there is the restriction that at least 1 unit of this expensive enzyme and at least 2.0 wt. % of a substrate protein concentration per 1 g of substrate protein are required for gelation. Further, the animal-derived transglutaminase is calcium (Ca 2+ )-dependent so that its application is limited. 
     Because of the foregoing defects, processes for producing gelation products using animal-derived transglutaminases are impractical. 
     Also, in view of the above difficulties of applying animal-derived transglutaminases in an industrial setting, a microorganism-derived transglutaminase which is produced by the genus Streptoverticillium has previously been proposed by the present inventors in European Patent Publication No. 0 379 606Al. 
     SUMMARY OF THE INVENTION 
     As a result of farther extensive investigation which has been made in search of a broad spectrum of microorganisms for use in the production of a transglutaminase, it has been found that the microoganisms belonging to the genus Streptomyces are capable of producing transglutaminases which catalyze an acyl transfer reaction of the γ-carboxyamide group of a glutamine residue in a peptide or protein chain in the presence and absence of Ca 2+ . The present invention is based on these findings. 
     It is therefore one object of the present invention to provide a process for producing a transglutaminase which is free from problems such as quantity of supply, cost/performance, and ease of purification. 
     It is another object of the present invention to provide a process for producing a transglutaminase which has great practicality since no calcium is required for the reaction catalyzed by the transglutaminase. 
     The above and other objects, which will become more readily apparent hereinafter, have been achieved by a process for producing a transglutaminase which comprises culturing a microorganism belonging to the genus Streptomyces, which is capable of producing a transglutaminase and harvesting the transglutaminase from the culture obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the invention becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein: 
     FIGS. 1, 2, 3 and 4 show an optimum pH curve, optimum temperature curve, pH stability curve and temperature stability curve of Enzyme No. 83 of the present invention, respectively. FIGS. 5, 6, 7 and 8 show an optimum pH curve, optimum temperature curve, pH stability curve and temperature stability curve of Enzyme No. 466 of the present invention, respectively. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As specific examples of the microorganisms belonging to the genus Streptomyces which can be used in the present invention, the following Streptomyces sp. No. 83 (hereafter, referred to as Strain No. 83) and Streptomyces lavendulae No. 466 (hereafter, referred to as Strain No. 466) which the present inventors isolated from soil samples may be mentioned. 
     The bacteriological characteristics of these new strains are set forth below. The experimental procedures used for taxonomical identification were those described in Experimental Methods for Identification of Actinomycetes, Japan Society for Actinomyces Research (1985), Classification and Identification of Microorganisms, Gakkai Shuppan Center (1975), and Experimental Methods for Chemical Classification of Microorganisms, Gakkai Shuppan Center (1982). 
     As references for classification and identification, Bergey&#39;s Manual of Determinative Bacteriology 8th Ed. (1974), Determinative Bacteriology 7th Ed. and 8th Ed., International Journal of Systematic Bacteriology 19, (1969) and 28 (1978), and Experimental Methods for Identification of Actinomycetes (1985) were used. As to colors, JIS Standard Color Cards, Japan Standards Association (1972), were referred to. 
     Bacteriological characteristics of Strain No. 83 and Strain No. 466 a. Morphologic characteristics 
     The morphologic characteristics are shown in Table 1. 
     
                       TABLE 1                                                     
______________________________________                                    
Morphologic Characteristics                                               
                Strain No. 83                                             
                            Strain No. 466                                
______________________________________                                    
Sporulated mycelium                                                       
Mode of branching                                                         
                monopodial  monopodial                                    
Spore morphology                                                          
                straight (R),                                             
                            flexuous (F),                                 
                open loops  straight (R)                                  
                (RA)                                                      
Spores                                                                    
Number          ≧50  5-10                                          
Spore wall ornamentation                                                  
                smooth      smooth                                        
Shape           oblong˜oval                                         
                            oblong˜oval                             
Size, μ      0.8 × 0.8 - 1.6                                     
                            0.6 - 1.0 ×                             
                            1.0 - 1.6                                     
Motility        none        none                                          
Sporangium      none        none                                          
Vegetative mycelium                                                       
Fragmentation   not fragmented                                            
                            not fragmented                                
Sclerotium                                                                
Formation       none (ball-like                                           
                            none                                          
                mass)                                                     
Sporangiophore                                                            
Position        on aerial and                                             
                            on vegetative                                 
                vegetative  mycelia                                       
                mycelia                                                   
Vegetative mycelium                                                       
Growth          zigzag      zigzag                                        
Aerial mycelium                                                           
Growth          good        poor                                          
Mode of branching                                                         
                radial      radial                                        
Sporangiophore                                                            
Length          short       short                                         
Branching       dichotomous                                               
______________________________________                                    
 
    
     b. Cultural characteristics in terms of growth and color 
     The cultural characteristics in terms of growth and color of Strain No. 83 and Strain No. 466 on various media (incubated at 28° C. and observed for 30 days) are set forth in Tables 2 and 3, respectively. 
     
                                           TABLE 2                                 
__________________________________________________________________________
(Cultural Characteristics of Strain No. 83)                               
            Vegetative Mycelium,                                          
                       Aerial Mycelium,                                   
                                 Reverse Color of                         
                                            Diffusible                    
Medium      Growth and Color                                              
                       Growth and Color                                   
                                 Vegetative Mycelium                      
                                            Pigment                       
__________________________________________________________________________
Sucrose nitrate agar                                                      
             (+)         (+)     Ivory      none                          
            colorless  reddish brown                                      
Glycerin asparagine                                                       
            (++)        (++)     light yellow                             
                                            none                          
agar (ISP No. 5)                                                          
            colorless  white                                              
Starch inorganic salt                                                     
            (++)       (+++)     yellow     none                          
agar (ISP No. 4)       reddish brown                                      
                                 (5Y 9/4)                                 
                       (5YR 2/8)                                          
Tyrosine agar (modified                                                   
            (++)        (++)     reddish brown                            
                                            none                          
Okanishi medium)       white     (2.5YR 6/3)                              
Yeast molt agar                                                           
            (+++)      (+++)     yellow     none                          
(ISP No. 2) colorless  Reddish brown                                      
                                 (2.5Y 8/6)                               
                       (5R 6/3)                                           
Bennet&#39;s agar                                                             
            (++)         (+)     yellow     none                          
                       white˜reddish                                
                                 (5Y 8/4)                                 
                       brown                                              
                       (5R 8/3)                                           
Peptone yeast iron                                                        
            (++)       (±)    yellowish brown                          
                                            none                          
agar (ISP No. 6)                                                          
            brown                (10YR 6/4)                               
            (2.5Y 4/4)                                                    
Peptone yeast                                                             
            (+++)      (++ +)    yellow     none                          
starch agar colorless  reddish brown                                      
                                 (2.5Y 8/6)                               
                       (5R 6/3)                                           
__________________________________________________________________________
 ±: Sparse                                                             
 +˜+++: Poor to luxuriant                                           
 
    
     
                                           TABLE 3                                 
__________________________________________________________________________
(Cultural Characteristics of Strain No. 466)                              
            Vegetative Mycelium,                                          
                       Aerial Mycelium,                                   
                                 Reverse Color of                         
                                            Diffusible                    
Medium      Growth and Color                                              
                       Growth and Color                                   
                                 Vegetative Mycelium                      
                                            Pigment                       
__________________________________________________________________________
Sucrose nitrate agar                                                      
             (+)       white     colorless  none                          
            colorless                                                     
Glycerin asparagine                                                       
            (++)       (+)       scarlet    light                         
agar (ISP No. 5)                                                          
            scarlet    pinkish   (2.5R 6/8) yellowish                     
            (2.5R 6/8) white                brown                         
Starch inorganic salt                                                     
            (++)       (+)       yellowish brown                          
                                            none                          
agar (ISP No. 4)                                                          
            scarlet    pinkish   (5Y 8/2)                                 
            (center    white                                              
Tyrosine agar (modified                                                   
            (++)       (+)       brown      brown                         
Okanish medium         brown     (2.5YR 3/2)                              
Nutrient agar                                                             
             (+)       (-)       brown      brown                         
            light brown          (2.5YR 4/4)                              
Yeast molt agar                                                           
            (++)       (±)    (7.5Y 6/5) light                         
(ISP No. 2) colorless                       yellowish                     
                                            brown                         
Bennet&#39;s agar                                                             
            (++)       (±)               none                          
            scarlet                                                       
Peptone yeast iron                                                        
            (++)       (-)       yellowish brown                          
                                            none                          
agar (ISP No. 6)                                                          
            yellowish brown                                               
                       colorless (10Y 7/4)                                
            (10Y 7/4)                                                     
Peptone yeast                                                             
            (++)       (+)       scarlet    light                         
starch agar colorless˜                                              
                       pinkish   (7.5Y 5/10)                              
                                            yellowish                     
            scarlet    white                brown                         
__________________________________________________________________________
 ±: Sparse                                                             
 +˜+++: Poor to luxuriant                                           
 
    
     c. Physiologic characteristics 
     The temperature range for growth and other characteristics such as gelatin liquefaction, starch hydrolysis, skin milk coagulation/peptonization, melanoid pigment production and hydrogen sulfide production of the respective strains are shown in Table 4. The carbon source assimilation spectrum (Pridham &amp; Gottlieb basal agar) of each strain is shown in Table 5. 
     d. Chemical characteristics 
     The results of analysis for cell wall amino acid composition and intracellular diaminopimelic acid are shown in Table 4. 
     
                       TABLE 4                                                     
______________________________________                                    
               Strain No. 83                                              
                         Strain No. 466                                   
______________________________________                                    
Temperature range for growth                                              
                 15-37       15-39                                        
(°C.)                                                              
Optimal temperature for                                                   
                 30-34       32-37                                        
growth (°C.)                                                       
Hydrolysis of starch                                                      
                 +           +                                            
Coagulation of skim milk                                                  
                 -           -                                            
Peptonization of skim milk                                                
                 -           +                                            
Production of melanoid                                                    
                 -           +                                            
pigment                                                                   
(Okanishi method)                                                         
Production of hydrogen sulfide                                            
                 not produced                                             
                             not produced                                 
Liquefaction of gelatin                                                   
                 negative    negative                                     
Reduction of nitrate (ISP                                                 
                 positive    negative                                     
No. 6)                                                                    
NaCl tolerance (peptone yeast                                             
extract starch)                                                           
4%               growth      growth                                       
7%               no growth   no growth                                    
Catalase         produced    produced                                     
Cell wall analysis                                                        
LL-diaminopimelic acid                                                    
                 present     present                                      
meso-DAP         absent      absent                                       
Total cell sugar Rham, Gal, Rib                                           
                             Rib                                          
Cell well amino acids                                                     
                 Lys, Gly, Asp                                            
                             Lys, Gly, Asp                                
Cell wall sugar  Rham, Gal   none                                         
Gram&#39;s stain     +           +                                            
Acid fastness    none        none                                         
Dissolution of calcium malate                                             
                 ++          +                                            
______________________________________                                    
 Rham: rhamnose                                                           
 Gal: galactose                                                           
 Rib: Ribose                                                              
 Lys: lysine                                                              
 Gly: glycine                                                             
 Asp: aspartic acid                                                       
 
    
     
                       TABLE 5                                                     
______________________________________                                    
(Pridham &amp; Gottlieb agar medium)                                          
            Strain No. 83                                                 
                     Strain No. 466                                       
______________________________________                                    
Glucose       ++         ++                                               
D-Xylose      -          -                                                
L-Arabinose   -          -                                                
L-Rhamnose    +          -                                                
D-Fructose    +          -                                                
D-Galactose   -          -                                                
Raffinose     -          -                                                
D-Mannitol    -          -                                                
i-Inositol    -          -                                                
Salicin       ++         -                                                
Sucrose       -          -                                                
Starch        +++        +++                                              
______________________________________                                    
 +++˜+: Strongly utilized˜utilized                            
 ±: doubtfully utilized                                                
 -: not utilized                                                          
 
    
     Thus, these strains contain diaminopimelic acid in the cell wall and LL-diaminopimelic acid intracellularly but did not contain meso-diaminopimelic acid. 
     (1) Identification of Strain No. 83 
     Excepting the rare occurrence of open loops (RA), the spore chains are predominantly linear and markably elongated (arthrospore type chains of 50-80 spores), forming a ball-like mass depending on media. The strain produces abundant vegetative hyphae on yeast extract-containing media (e.g., ISP No. 2 medium), which are characterized by being velvety or downy and azuki-colored (reddish brown). The existence of LL-diaminopimelic acid and the absence of meso-diaminopimelic acid suggest that it belongs to cell wall type I. As to sugars, galactose and rhamnose were detected but neither arabinose nor xylose was found. These and other characteristics such as fragmentation of hyphae, spore chain morphology, spore motility, aerial mycelium, whorl formation, acid fastness and catalase production suggested that the strain belongs to the genus Streptomyces. 
     Meanwhile, the carbon assimilation spectrum of the strain is relatively narrow, with starch, glucose, salicin, rhamnose and fructose (weak) only being assimilated. The above and other characteristics of the strain suggested that it is akin to Streptomyces cinnamonenois, Streptomyces nojiriensis and Streptomyces diastaticus. However, the strain differentiates itself clearly from the above-mentioned species in that it produces melanoid pigments and does not utilize rhamnose. Therefore, the strain was identified to belong to a new species of the genus Streptomyces and designated Streptomyces sp. No. 83. 
     (2) Identification of Strain No. 466 
     The aerial mycelium is usually so sparse that it looks like the vegetative mycelium exposed on the surface. Its color is scarlet. The colony surface is radial, filmy and hard, with hyphae characteristically extending well into the agar. As to spore chain morphology, comparatively short chains of arthrospores (5-10 spores) are produced on Pridham-Gottlieb starch medium but spore chains on most other media are not uniform, being spherical or hooked, with the hyphal end being indented in the form of a hump or branched. As to the cell wall composition, LL-diaminopimelic acid was detected but meso-diaminopimelic acid was absent, indicating that it corresponds to cell wall type I. The findings that the strain utilizes glucose and starch only and tolerates not more than 4% NaCl as well as its straight or digital spore morphology, red-series color of aerial mycelium and melanoid pigment production suggest that it is a strain of Streptomyces xanthophaeus or Streptomyces flavotricini according to Bergey&#39;s Manual, 8th Ed, or Streptomyces lavendulae according to the updated edition thereof, viz. Bergey&#39;s Manual of Systematic Bacteriology (1989). Therefore, the strain was identified to belong to the genus Streptomyces and designated Streptomyces lavendulae No. 466. 
     Incidentally, Streptomyces sp. No. 83 and Streptomyces lavendulae No. 466 have been deposited with the Fermentation Research Institute, Agency of Industrial Science and Technology 1-3, Higashi 1-chome, Tsukuba-shi, Ibaraki-ken 305, Japan on Aug. 13, 1990 under the respective deposit number of FERM No. P-11656 (FERM No. BP-3505 under Budapest Treaty) and FERM No. P-11657 (FERM No. BP-3506 under Budapest Treaty), respectively. 
     For the purposes of the present invention, any microorganism belonging to the genus Streptomyces, which is capable of producing transglutaminases can be successfully employed, preferably Streptomyces sp. No. 83 (Strain No. 83) and Streptomyces lavendulae No. 466 (Strain No. 466) described above. 
     Methods for culture, purification etc., which comprise culturing these microorganisms and harvesting transglutaminase (hereafter, referred to as BTGase) will be described below. 
     For the purposes of the present invention, any culturing mode of liquid culture and solid culture can be performed, but from an industrial standpoint, it is advantageous to perform deep aerial spinner culture. As culture sources to be used, there can be used carbon sources, nitrogen sources, inorganic salts and other trace nutrient sources conventionally used for culture of microorganisms; in addition thereto, all nutrient sources can be employed as long as they are utilizable by microoganisms belonging to the genus Streptomyces. As the carbon sources for media, there can be used, singly or in combination, glucose, sucrose, rastagen, glycerin, dextrin, starch, etc. and in addition thereto, fatty acids, oils and fats, organic acids, etc. As the nitrogen sources, any of inorganic nitrogen sources and organic nitrogen-sources can be used. As the inorganic nitrogen sources, there can be used ammonium nitrate, ammonium sulfate, sodium nitrate, ammonium chloride, etc. 
     Further as the organic nitrogen sources there can be used, for example, powder of soybean, rice, sweet corn and wheat etc., bran and defatted meal, and corn steep liquor, peptone, meat extract, casein, amino acids, yeast extract, etc. As the inorganic salts and the trace nutrient sources, there can be used salts of phosphoric acid, magnesium, potassium, iron, calcium, zinc, etc., and any other materials that can accelerate growth of the bacteria or production of BTGase such as vitamins, nonionic surfactants, defoaming agents, etc., if necessary. Culture may be performed under aerobic conditions at a culture temperature within such a range that the bacteria grow to product BTGase, preferably at 25° to 35° C. A time period for the culture varies depending upon conditions but the culture may be performed until BTGase is best produced, generally for about 2 to 4 days. In the case of liquid culture, BTGase is dissolved in the culture solution and can be harvested from the culture filtrate obtained by removing solid contents from the culture solution after completion of the culture. 
     For purification of BTGase from the culture filtrate, any method generally used for purification of enzymes can be used. 
     For example, there can be used treatment methods with an organic solvent such as ethanol, acetone, isopropyl alcohol, etc.; salting out using ammonium sulfate, sodium chloride, etc., dialysis, ultrafiltration, ion exchange chromatography, adsorption chromatography, gel filtration, adsorbents, isoelectric point fractionation, etc. Further, in the case where the purity of BTGase is increased by the use of these methods in suitable combination, the methods can be performed in such a combination. From the enzyme obtained by these methods, liquid or solid BTGase can be obtained by methods of ultrafiltration condensation, reverse osmosis condensation, drying under reduced pressure, freeze drying or spray drying, by adding a variety of salts, sugars, proteins, lipids, surfactants, etc., as stabilizers or without adding them. 
     Measurement of the activity of BTGase is carried out by performing a reaction using benzyloxycarbonyl-L-glutaminyl glycine and hydroxylamine as substrates in the absence of Ca 2+ , forming an iron complex with the resulting hydroxamic acid in the presence of trichloroacetic acid, measuring absorption at 525 nm and determining the amount of hydroxamic acid by a calibration curve to calculate the activity. The BTGase activity is measured by the method described below, unless otherwise indicated. 
     Measurement of Activity 
     Reagent A 
     0.2 M Tris-hydrochloride buffer (pH 6.0) 
     0.1 M hydroxylamine 
     0.01 M reductive glutathione 
     0.03 benzyloxycarbonyl-L-glutaminyl glycine 
     Reagent B 
     Reagent B is made of equal volumes of the following component. 
     3 N hydrochloric acid 
     12% trichloroacetic acid 
     5% FeCl 3 .6H 2  O (dissolved in 0.1 N-HCl) 
     To 0.05 ml of an enzyme solution is added 0.5 ml of Reagent A and they are mixed with each other. After reacting at 37° C. for 10 minutes, Reagent B is added thereto to discontinue the reaction and form an Fe complex. Thereafter, absorbance is measured at 525 nm. As a control, absorbance is measured after reacting a previously thermally inactivated enzyme solution in a similar manner and a difference in absorbance between the control and the enzyme solution is measured. Separately, a calibration curve is prepared using L-glutamic acid γ-monohydroxamic acid instead of the enzyme solution, and the amount of hydroxamic acid produced is determined by the difference in absorbance described above. An enzyme activity which produces 1 μmol of hydroxamic acid per 1 minute is defined as 1 unit. 
     Enzymological properties of the thus obtained purified BTGases, namely, transglutaminase of Streptomyces sp No. 83 (named Enzyme No. 83) and transglutaminase of Streptomyces lavendulae No. 466 (named Enzyme No. 466) are described below. 
     a) Optimum pH 
     In the case of using benzyloxycarbonyl-L-glutaminyl glycine, and hydroxylamine as substrate, each optimum pH of Enzyme No. 83 and Enzyme No. 466 lies in a range of approximately 6 to 7 upon the reaction at 37° C. for 10 minutes (shown in FIGS. 1 and 5). 
     b) Optimum temperature 
     In the case of using benzyloxycarbonyl-L-glutaminyl glycine and hydroxylamine as substrates, each optimum temperature of Enzyme No. 83 and Enzyme No. 466 lies at about 40°˜45° C. upon the reaction of pH 7 for 10 minutes (shown in FIGS. 2 and 6). 
     c) pH Stability 
     By treatment at 37° C. for 10 minutes, both Enzyme No. 83 and Enzyme No. 466 are stable at pH of 6 to 9 (shown in FIGS. 3 and 7). 
     d) Temperature stability 
     By treatment at pH 7 for 10 minutes, Enzyme No. 83 retains 100 activity at 40° C. and 55% at 50° C.: and Enzyme No. 466 retains 94% activity at 40° C. and 32% at 50° C. (shown in FIGS. 4 and 8). 
     e) Substrate specificity 
     Using each BTGase, reactions of various synthetic substrates with hydroxylamine were examined. No BTGase reacts with the synthetic substrates benzyloxycarbonylasparaginyl glycine, benzyloxycarbonyl glutamine and glycylglutaminyl glycine. However, the reactivity is the highest when the synthetic substrate is benzyloxycarbonylglutaminyl glycine. In this case, the concentration of various synthetic substrates is 5 mM. The results are shown in Table 6. In the table, CBZ, Gln, Gly and Asn are abbreviations for benzyloxycarbonyl group, glutaminyl group, glycyl group and asparaginyl group, respectively. 
     
                       TABLE 6                                                     
______________________________________                                    
Substrate       Enzyme No. 83                                             
                            Enzyme No. 466                                
______________________________________                                    
CBZ--Gln--Gly   100         100                                           
CBZ--Gln--Gly--OEt                                                        
                61          65                                            
CBZ--Gln--Gln--Gly                                                        
                49          35                                            
CBZ--Gly--Gln--Gly--Gly                                                   
                10          18                                            
CBZ--Gln         0           0                                            
CBZ--Asn--Gly    0           0                                            
Gly--Gln--Gly    0           0                                            
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     f) Influence of metal ions 
     Various metal ions were added to the activity measurement system in a concentration of 1 mM (the results are shown in Table 7). In all BTGases, the activity is inhibited by Cu 2+ , Zn 2+   and Pb 2+ . 
     
                       TABLE 7                                                     
______________________________________                                    
            Enzyme No. 83                                                 
                        Enzyme No. 466                                    
Metal Ion   (%)         (%)                                               
______________________________________                                    
None        100         100                                               
CaCl.sub.2  101         99                                                
BaCl.sub.2  100         100                                               
CoCl.sub.2  100         98                                                
CuCl.sub.2   89         90                                                
FeCl.sub.3   93         97                                                
KCl         104         101                                               
MgCl.sub.2  102         99                                                
MnCl.sub.2  102         99                                                
NaCl        102         98                                                
NiCl.sub.2  101         99                                                
PbCl.sub.2   59         32                                                
SrCl.sub.2  100         97                                                
ZnCl.sub.2   36         10                                                
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     g) Influence of inhibitor 
     Each inhibitor was added in a concentration of 1 mM. After allowing the mixture to stand at 25° C. for 30 minutes, the activity was measured (the results are shown in Table 8). In all BTGases, the activity is inhibited by p-chloromercury benzoic acid (simply referred to as PCMB), N-ethylmaleimide (simply referred to as NEM) and monoiodoacetic acid. 
     
                       TABLE 8                                                     
______________________________________                                    
Inhibitor     Enzyme No. 83 Enzyme No. 466                                
______________________________________                                    
None          100           100                                           
EDTA          103           108                                           
PCMB           86            28                                           
NEM            10            5                                            
Monoiodoacetic acid                                                       
               92            87                                           
PMSF          101           103                                           
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     In Table 8, PMSF is the abbreviation for phenylmethylsulfonyl fluoride. 
     h) Isoelectric point 
     According to ampholine isoelectric point electrophoresis, isoelectric points, pI of Enzyme No. 83 and pI of Enzyme No. 466 are at approximately 10 and 6.8, respectively. 
     i) Molecular weight 
     According to SDS disc electrophoresis, molecular weight of Enzyme No. 83 and Enzyme No. 466 are approximately 39,000. 
     Next, properties of BTGases are compared to those of guinea pig liver-derived transglutaminase. The guinea pig liver-derived transglutaminase was prepared by the method described in Connellan et al., Journal of Biological Chemistry, Vol. 246, No. 4, pp. 1093-1098  (1971). In Table 9, comparison in enzymological properties is shown and influence of Ca 2+  on activity is shown in Table 10. As will be apparent from Tables 9 and 10, various differences in enzymological properties are noted between transglutaminase of guinea pig liver (hereafter, referred to as MTGase) which has been mainly investigated heretofore and BTGases derived from the genus Streptomyces: in particular, differences are noted in temperature stability, molecular weight, isoelectric point and substrate specificity. Further, a difference is noted in that the BTGases of the present invention act in the presence and absence of Ca 2+ . Therefore, the respective enzymes of the present invention are different from MTGase in their properties. 
     
                       TABLE 9                                                     
______________________________________                                    
              Enzyme Enzyme                                               
              No. 83 No. 466    MTGase                                    
______________________________________                                    
Optimum pH      ca. 6-7  ca. 6-7     6                                    
pH Stability    6-9      6-9        6-7.5                                 
Optimum temperature                                                       
                ca.      ca. 40-45° C.                             
                                    50-55° C.                      
                40-45° C.                                          
Temperature stability (%)                                                 
40° C. residual rate                                               
                100      94          96                                   
50° C. residual rate                                               
                55       32          40                                   
Molecular weight                                                          
                ca. 39,000                                                
                         ca. 39,000 ca. 90,000                            
Isoelectric point                                                         
                ca. 10   ca. 6.8      4.5                                 
Substrate specificity (%)                                                 
CBZ--Gln--Gly   100      100        100                                   
CBZ--Gln--Gly--OEt                                                        
                61       65         122                                   
CBZ--Gln--Gln--Gly                                                        
                49       35         288                                   
CBZ--Gly--Gln--Gly--Gly                                                   
                10       18         126                                   
CBZ--Gln         0        0          0                                    
CBZ--Asn--Gly    0        0          0                                    
Gly--Gln--Gly    0        0          0                                    
______________________________________                                    
 
    
     
                       TABLE 10                                                    
______________________________________                                    
         Enzyme No. 83                                                    
                      Enzyme No. 466                                      
                                    MTGase                                
Metal Ion                                                                 
         (%)          (%)           (%)                                   
______________________________________                                    
None     99           99             0                                    
1 mM CaCl.sub.2                                                           
         99           98             39                                   
5 mM CaCl.sub.2                                                           
         100          100           100                                   
______________________________________                                    
 
    
     The present invention is now illustrated in greater detail with reference to the following Examples, but it should be understood that the present invention is not deemed to be limited thereto. 
     EXAMPLE 1 
     Streptomyces sp No. 83 was inoculated on 200 ml of medium (pH 7) having a medium composition of 0.2% of polypeptone, 0.5% of glucose, 0.2% of dipotassium phosphate and 0.1% of magnesium sulfate followed by culturing at 30° C. for 48 hours. The obtained seed culture solution was added to 20 l of a medium (pH 7) containing 2.0% of polypeptone, 2.0% of rastagen (trademark, manufactured by Nichiden Kagaku K.K.), 0.2% of dipotassium phosphate, 0.1% of magnesium sulfate, 0.2% of yeast extract and 0.05% of Adekanol as a defoaming agent (trademark, manufactured by Asahi Denka Kogyo K.K.) followed by culturing at 30° C. for 3 days. After filtering, 18.5 l of the culture solution was obtained. The activity was 0.71 U/ml. 
     The culture solution was adjusted with hydrochloric acid to pH of 6.5 and passed through a column of CG-50 (trademark, manufactured by Organo Co., Ltd.), which had been previously equilibrated with 0.05 M phosphate buffer (pH 6.5). By this operation, transglutaminase was adsorbed. After washing protein impurities out with the same phosphate buffer solution, a density gradient of 0.05 to 0.5 M was prepared by the same buffer, through which the system was passed. The eluate was fractionated and recovered, and the fractions having a high specific activity were collected. After the system was diluted to have a conductivity of 10 ms or less, it was passed through a column of blue Sepharose. By this operation, transglutaminase was adsorbed. After washing protein impurities out with 0.05 M phosphate buffer (pH 7), a density gradient of 0 to 1 M was prepared by sodium chloride, through which the system was passed. The eluate was recovered and fractions having a high specific activity were collected. The fractions were desalted and rechromatographed on a column of CG-50 to fractionate the eluate. As a result, the active fraction eluted as a single peak. The specific activity was 356 times that of the culture filtrate and the recovery rate was 43%. 
     EXAMPLE 2 
     Streptomyces lavendulae No. 466 was inoculated into 200 ml of the same preculture medium as used in Example 1 and cultured at 30° C. for 48 hours. The resulting seed culture solution was added to 20 l of a medium (pH 7) containing 2.0% of polypeptone, 2.0% of glycerin, 0.2% of dipotassium phosphate, 0.1% of magnesium sulfate, 0.2% of yeast extract and 0.05% of Adekanol, which was then cultured at 30° C. for 3 days. The resulting culture broth was filtered to give 18.5 l of the culture filtrate. The activity of this culture solution was 2.47 U/ml. 
     Using a UF 6000 membrane, the culture solution was desalted and concentrated and the concentrate was adjusted to pH 7.0 with hydrochloric acid and passed through a column of DEAE-Cellulofine (trademark, manufactured by Seikagaku Kogyo), which had been previously equilibrated with 0.005 M phosphate buffer (pH 7.0). By this operation, transglutaminase was adsorbed on the column. The column was first washed with the same phosphate buffer solution to remove protein impurities and, then, elution was carried out with the same buffer on a density gradient of 0.005 to 0.5 M. The eluate was collected in fractions and the fractions having a high specific activity were collected. Then, using blue Sepharose and CG-50, the enzyme was purified as in Example 1 to give a pure enzyme giving a single peak in SDS disk electrophoresis. The specific activity relative to the culture filtrate was 169 times and the recovery rate was 37%. 
     As is apparent from above, the microorganism-derived BTGase of the present invention can be supplied at low cost and can be easily purified and therefore, is highly practical. 
     It is also advantageous that by the use of a BTGase according to the present invention, the research and development on various uses such as a food manufacturing or a medical treatment can be accelerated. 
     While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.