[Ferrireductase from Pichia guilliermondii: properties and regulation of activity and synthesis]. / Ferireduktaza Pichia guilliermondii: vlastyvosti i rehuliarsiia aktyvnosti ta syntezu.

Properties of Pichia guilliermondii ferrireductase of the crude extracts and ammonium sulfate preparations were studied. NADH and Cu (II) ions are necessary for ferrireductase activity. Mg (II) also stimulates this reaction while oxygen acts as a slight inhibitor. Ferrireductase reduces Fe (III) in complex with citrate, iron-binding peptide from the culture medium of P. guilliermondii, rhodotorulic acid, coprogen, desferrioxamine B and EDTA. Mutants rib80, rib81 and hit of Pichia guilliermondii that have damaged system of riboflavin biosynthesis and iron transport regulation are characterized by high ferrireductase activity. Iron through negative feed-back mechanism regulates activity of ferrireductase synthesis in P. guilliermondii, Candida famata, Candida krusei, Candida boidinii, but not in Pichia pinus and Hansenula polymorpha.

[Study of the regulation of the synthesis and activity of IMP-dehydrogenase in the yeast Pichia guilliermondii]. / Doslidzhennia rehuliatsiï syntezu i aktyvnosti IMF-dehidrohenazy u drizhdzhiv Pichia guilliermondii

Activity of IMP-dehydrogenase was studied in the cells of P. guilliermondii ATCC 9058 from different growth phase; the yeast was cultivated in iron-rich and iron-deficient media. The highest activity of the enzyme was found in the iron-rich cells from the logarithmic growth phase. In the iron-deficient cells synthetizing great amounts of riboflavin the IMP-dehydrogenase activity was somewhat higher in negative growth acceleration phase than that of iron-rich cells from the same stage. Guanine considerably represses synthesis of IMP-dehydrogenase in the cells of the mutant P. guilliermondii Y-2031 with the blocked GMP-synthetase. In the iron-deficient cells no changes in the character of IMP-dehydrogenase synthesis regulation were found in comparison with the iron-rich cells. 5'-GMP, 5'-GDP and 5'-GTP considerably inhibit IMP-dehydrogenase activity of the cell-free preparations of the yeast P. guilliermondii. 5'-AMP, 5'UMP and 5'-CMP slightly affect the enzyme activity. Guanine inhibits LMP-dehydrogenase activity in experimeents in vivo with the guanine- and arginine-requiring "Y" 2031/arg. Thus, synthesis of guanylic acid in the yeast P. guilliermondii is regulated by means of two mechanisms repression of IMP dehydrogenase synthesis and inhibition of the activity of this enzyme by guanyl compounds.