CYTOSININE - PYRIDOXAL-PHOSPHATE TAUTOMERASE, A NEW ENZYME IN THE BLASTICIDIN-S BIOSYNTHETIC-PATHWAY

Cytosinine-the nucleoside portion of blasticidin S-and pyridoxal phosp hate were incubated with cell-free extracts of Streptomyces griseochro mogenes prepared in D2O. H-2 NMR analysis of recovered cytosinine show ed it to contain deuterium enrichments at H-4' and H-2' No exchange wa s observed with either boiled extract or from cytosinine and pyridoxal phosphate alone. These results reveal the presence of a tautomerase a ctivity that contributes to the net transamination at C-4' in the conv ersion of cytosylglucuronic acid to blasticidin S, and its discovery s upports the role of cytosinine as a biosynthetic intermediate.