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Cytosylglucuronic acid synthase (cytosine: UDP-glucuronosyltransferase), the first prokaryotic UDP-GT and a key enzyme in the biosynthesis of the antibiotic blasticidin S, was purified 870-fold. It has optimum activity at a pH of 8.4 to 8.6, Kms of 6.0 (UDP-glucuronic acid) and 243 (cytosine) microM, and a maximum rate of metabolism of 14.6 mumol/min/mg. The apparent M(r) is 43,000. Activity was slightly enhanced by Mg2+ or Ca2+ but was not inhibited by EDTA. Activity was strongly inhibited by UDP. Cytosylglucuronic acid differs from eukaryotic UDP-glucuronosyltransferases in being a soluble protein with no apparent phospholipid requirement.

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s . Can. J. Chem. 72,6 (1994).Intermediates in the biosynthesis of blasticidin S and its nucleoside co-metabolites were detected by altering fermentation conditions. Inhibitors of specific types of biochemical reactions that were expected to be involved in blasticidin biosynthesis were fed to Streptomyces griseochromogenes, in some cases with the inclusion of large quantities of the primary precursors of blasticidin S. The types of reactions and inhibitors used were (1) transaminase (aminooxyacetic acid and 2-methylglutamate), (2) amidotransferase (azaserine and 6-diazo-5-0x0-L-norleucine), (3) arginine biosynthesis (arginine hydroxamate), and (4) methyltransferase (ethionine). These manipulations apparently distorted the pools of precursors and (or) intermediates, and led to substantial accumulations of three known, previously minor, metabolites of S. griseochromogenes, cytosylglucuronic acid, pentopyranine C, and demethylblasticidin S, and of two new ones, pentopyranone and isoblasticidin S. New cytosyl metabolites were detected by HPLC with photodiode array detection. Fermentations to which arginine hydroxamate and cytosine had been added also produced three aberrant metabolites that were derived from pentopyranone and arginine hydroxamate. [Traduit par la redaction]