Degradation of intracellular proteins at different stages of growth of Saccharomyces cerevisiae

The rate of degradation of intracellular proteins at different growth stages of Saccharomyces cerevisiae yeast was determined. It has been demonstrated that the rate of degradation of intracellular proteins increases 2--3-fold at the late exponential phase. The increase was accompanied by corresponding changes in the activities of yeast proteinases A and B. In the presence of specific yeast proteinase inhibitors (pepstatin and phenylmethylsulfonyl fluoride) the rate of protein degradation in vivo decreased. The intermediate products of cell protein degradation have been found. These TCA-insoluble products could be extracted by various solvent systems. Their subsequent brakdown was suppressed by specific proteinase inhibitors.