[Biosynthesis of 6,7-dimethyl-8-ribityllumazine in yeast extracts of Pichia guilliermondii].

The effects of some hexoses, pentoses, their phosphoric esters, ribitol and pyruvate on the synthesis of 6.7-dimethyl-8-ribityllumazine in extracts of prototrophic strain and riboflavin-deficient mutants of the yeast Pichia guilliermondii ATCC 9058 were studied. Incubation of dialyzed cell extracts of the mutant strain RG123 (rib7, his-) with blocked riboflavin syntase in the presence of 2.5-diamino-6-hydroxy-4-ribosylaminopyrimidine-5'-phosphate, NADPH and ribose-5-phosphate results in production of 6.7-dimethyl-8-ribityllumazine. In similar experiments with cell extracts of the prototrophic strain 6.7-dimethyl-8-ribityllumazine and riboflavin were formed. Consequently all the reactions of vitamin B2 biosynthesis occurred under these conditions. Glucose 6-phosphate and fluctose 6-phosphate weakly activated the biosynthesis of 6.7-dimethyl-8-ribityllumazine, while ribose, ribitol, fructose, glucose and pyruvate had no effect on this process. When cell extracts of mutant strains of genotypes rib5 and rib6 with a blocked enzyme(s) of the fourth step of flavinogenesis were incubated in the presence of ribose 5-phosphate no 6.7-dimethyl-8-ribityllumazine formation took place. It is concluded than in the P. guilliermondii yeast ribose 5-phosphate or its metabolite can donate carbon atoms for 6.7-dimethyl-8-ribityllumazine biosynthesis from its pyrimidine precursor.