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.
Riboflavin 5′-Hydroxymethyl Oxidation
Vitamin B2-aldehyde-forming enzyme catalyzes oxidation of the 5′-hydroxymethyl of riboflavin to the formyl group. We have purified the enzyme from the culture media ofSchizophyllum commune (ATCC 38719) by modifying the procedure of Tachibana and Oka (Tachibana, S., and Oka, M. (1981)J. Biol. Chem. 256, 6682–6685) for cell-free extract. By SDS-polyacrylamine gel electrophoresis, the enzyme appears to be 78 kDa. The enzyme has a blocked amino terminus, so fragments were obtained by cleaving the purified enzyme with lysyl endopeptidase. Selected peptides were sequenced from their amino termini. We have isolated a full-length cDNA clone using a DNA hybridization probe amplified by polymerase chain reaction with two degenerate oligonucleotide primers, the design of which was based on one of the partial amino acid sequences. From the cDNA clone, it is evident that the enzyme has a Ser/Thr-rich fragment near the COOH-terminal Asp. The enzyme was determined to be a glycoprotein; however,O-deglucosylation only slightly affects activity. Computer searches showed that the B2-aldehyde-forming enzyme has little homology with other proteins, but domain motifs may reflect N-myristoylation of a dehydrogenase with a signature similar to 4Fe-4S ferredoxins. The enzyme cDNA was subcloned into a Pichia expression vector pPIC9K to produce a recombinant protein which exhibited B2-aldehyde-forming enzyme activity.
A new class of numerical sequences and its applications to sine and cosine series
First, it is proved that the class of classical quasi-monotone sequences is not comparable to the newly defined class of sequences of ‘rest bounded variation’. Considering this result, we prove three sample theorems for sequences of rest bounded variation, being analogues of the theorems proved earlier for monotone or quasi-monotone sequences. One of them gives a partial answer to a question raised by R. P. Boas Jr.