Fungal riboflavin 5'-hydroxymethyl dehydrogenase catalyzes formation of both the aldehyde (riboflavinal) and the acid (riboflavinoic acid).
The purified enzyme from Schizophyllum commune that readily catalyzes the oxidation of the 5'-hydroxymethyl function of riboflavin (vitamin B2) with a redox dye and O2 to form the 5'-aldehyde can more slowly further oxidize the 5'-aldehyde to the 5'-acid. Hence, the formation of these so-called 'schizoflavins' can be accounted for by the action of one enzyme.
Occurrence of a vitamin B2-aldehyde-forming enzyme in Schizophyllum commune.
Vitamin B2-aldehyde-forming enzyme from riboflavin was purified about 1,400-fold from a cell-free extract of Schizophyllum commune by ammonium sulfate saturation fractionation, ethanol fractionation, and column chromatographies on DEAE-Sephacel and Sephadex G-100. The purified enzyme was shown to be homogeneous on polyacrylamide disc gel electrophoresis, and most active at about pH 5.5. The molecular weight was determined to be approximately 60,000-62,000 by gel filtration. The enzyme was specific for riboflavin; other compounds such as alcohol, sugar, phenol or nucleoside were not oxidized by this enzyme, as far as tested. alpha-NAD+, beta-NAD+, alpha-NADP+, beta-NADP+, FMN, FAD, and cytochrome c were not active as an electron acceptor. 2,6-Dichlorophenolindophenol served as a good electron acceptor, and phenazine methosulfate and methylene blue were found to be somewhat effective. The enzyme stoichiometrically oxidized 1 mol of riboflavin with 1 mol of 2,6-dichlorophenolindophenol as electron acceptor. The enzyme reaction was completely inhibited by 10 microM Hg2+, but was not inhibited by sulfhydryl reagent, carbonyl reagent, and metal chelator. Kinetics analysis gave a Km value of 17 microM for riboflavin.
The behaviour of mercury compounds in soil
The uses of inorganic compounds of mercury for the control of plant pests is reviewed, and a summary of the relevant chemical and physical properties of the compounds concerned is given. On chemical evidence a working hypothesis is propounded showing that all compounds may be expected to decompose into metallic mercury. 
 
 
 
A pot technique is described by means of which a correlation can be obtained between the effective mercury content of a given soil sample and the rate of growth of wheat seedlings. The mathematical treatment of the results is described, and the validity of the pot technique is verified by statistical analysis of results. Using the pot technique it is shown that volatilization losses are insignificant but that mercury is slowly rendered ineffective by the formation of mercuric sulphide. The effect of sulphur-reducing bacteria is considered and the influence of Vibrio desulpkuricans on mercury is studied in detail. 
 
 
 
Experimental evidence obtained by the pot technique is produced to show that mercurous chloride slowly decomposes in the soil giving mercury and mercuric chloride, mercuric chloride rapidly decomposes into mercury and mercurous chloride, and other inorganic compounds decompose directly into mercury. The working hypothesis is substantiated in all major aspects. 
 
 
 
The uses and properties of the organo-mercury compounds are then discussed. Type compounds selected are ethyl mercury phosphate, phenyl mercury acetate and methoxyethyl mercury acetate. 
 
 
 
Using the pot technique it is shown that the formation of organo-mercury clays takes place and that these clays decompose giving metallic mercury. A mechanism is suggested.