Proteolysis in eukaryotic cells. Proteinase yscE, a new yeast peptidase

A new peptidase, which we call proteinase yscE, was purified from the yeast Saccharomyces cerevisiae. The enzyme cleaves the synthetic substrates Cbz-Gly-Gly-Leu-4-nitroanilide, Cbz-Ala-Ala-Leu-4-nitroanilide, and Suc-Phe-Leu-Phe-4-nitroanilide (Cbz and Suc are defined as benzyloxycarbonyl and succinyl, respectively) at the 4-nitroanilide bond and exhibits a slight activity against [3H]methylcasein. Optimum pH for cleavage of the chromogenic substrates is found to be in the range of 8.2 to 8.6. The purified enzyme has an apparent Stokes radius of Rs = 75.2 A as judged by gel chromatography and is composed of subunits. Mercurials were found to be strong inhibitors of the enzyme activity.