Inactivation of yeast enzymes by proteinase A and B and carboxypeptidase Y from yeast.

Changes in the activities of 15 different enzymes during incubation of a crude yeast extract with the purified yeast proteinases A and B, and carboxypeptidase Y, respectively, have been measured. The spectrum of action of the three proteinases on the enzymes measured differs significantly, increasing or decreasing their activities or having no effect. Incubation of purified cytoplasmic malate dehydrogenase or purified mitochondrial malate dehydrogenase with proteinases A and B results in selective inactivation of the cytoplasmic enzyme, whereas the mitochondrial activity is not affected. Carboxypeptidase Y has no effect on the activity of either dehydrogenase. The results support the idea of selective proteolysis as the mechanism of the earlier observed inactivation of cytoplasmic malate dehydrogenase, initiated by the addition of glucose to intact yeast cells grown on acetate as carbon source ("glucose effect").