Difference in pyruvate kinase regulation among three groups of yeasts.

Yeast pyruvate kinase (ATP : pyruvate 2-O-phosphotransferase EC 2.7.1.40) was classified into three groups based on the interaction with fructose-1,6-bisphosphate. The pyruvate kinases of Saccharomyces cerevisiae and Saccharomyces carlsbergensis were activated by fructose 1,6-bisphosphate in the concentration range tested (up to 10 mM) of the substrate, phosphoenolpyruvate; the enzymes of "fermentative Candida" (Candida tropicalis and Candida utilis) were affected by fructose 1,6-biphosphate only when the substrate concentration was below 2 mM. Although the pyruvate kinase of Candida lipolytica (a yeast belonging to "oxidative Candida") was also affected by fructose 1,6-bisphosphate, the degree of the activation was extremely small as compared with the above four yeasts. The pyruvate kinase of C. tropicalis was inhibited by ATP more strongly in the absence of fructose 1,6-bisphosphate than its presence. In the case of the C. lipolytica enzyme, however, the enzyme was inhibited to a lesser extent by ATP, and fructose 1,6-bisphosphate did not reverse the inhibitory effect of ATP. Time course changes of the enzyme levels in the yeasts grown on glucose and on ethanol indicate that the pyruvate kinases of S. cerevisiae and C. tropicalis can be controlled both by an allosteric mechanism and by changes in the enzyme concentration, although a marked difference was observed in the susceptibility to the allosteric effect by fructose 1,6-biphosphate between these fermentative yeasts. On the other hand, that of C. lipolytica would be controlled only by the latter mechanism.