[Effect of riboflavin analogs on Pichia guilliermondii growth].

The work was aimed at studying the biological activity of 32 structural riboflavin (RF) analogs substituted at positions 7, 8 and 10 as well as with a modified structure of the isoalloxazine cycle and the side D-ribityl chain. An RF-dependent mutant of the yeast Pichia guilliermondii MS1 was used as a test organism. The strain could grow in a medium without the vitamin in the presence of 2-thio-RF and analogs with esterified hydroxyls in the side chain, viz. tetraacetate and tetrabutyrate of RF. The antagonistic properties were distinctly displayed only by D-ribityl derivatives of vitamin B2 with a substitution of CF3, Cl, H, NH2 and N(CH3)2 for one or the both methyl groups. The inhibition indices for such analogs varied from 0.52 to 10.8. The action of the antivitamins on the yeast growth was competitively eliminated by adding RF to the growth medium. The antivitamin activity of an analog abruptly decreased or disappeared if (i) a bulky substituent such as N-piperidyl or hydroxyethylamine was incorporated at position 8 of an antimetabolite molecule, (ii) the D-ribityl side chain was substituted by a D-galactyl, D-sorbityl, L-ramnityl, 2-hydroxyethyl or methyl group and (iii) the structure of isoalloxazine cycle was modified. The analogs which were phosphorylated by RF kinase (ATP: RF-5'-phosphotransferase, EC 2.7.1.26) from P. guilliermondii were shown to be effective antivitamins. Therefore, the antagonistic effect of vitamin B2 analogs in yeast cells is realized at the level of coenzyme forms.