[Regulation of the activity and synthesis of enzymes participating in the formation of 6,7-dimethyl-8-ribityllumazine, a riboflavin precursor in yeast].

The properties of two flavinogenesis enzymes--synthase of the aliphatic precursor of riboflavin (APR-synthase) and 6.7-dimethyl-8-ribityllumazinesynthase (DMRL-synthase) of Pichia guilliermondii. It is established that DMRL-synthase, uses APR as a substrate which contains, evidently, a phosphate group. The value of Km for APR is equal to 0.7.10(-5) M, for 2.4-dihydroxy-5-amino-6-ribitylaminopyrimidine--1.25.10(-5) M. It is riboflavin but not FAD that inhibits the activity of DMRL-synthase; the value (I)0.5 is equal to 2.10(-5) M. DMRL, riboflavin, flavin mononucleotide and FAD do not affect the APR-synthase activity. In iron-deficient cells of P. guilliermondii, Torulopsis candida, Debaryomyces klöckeri and Schwanniomyces occidentalis realizing the oversynthesis of riboflavin there occurs derepression of DMRL-synthase and APR-synthase.