Hormone processing and membrane‐bound proteinases in yeast.

A search for maturating peptidases of the precursor protein of the mating hormone (pheromone) alpha‐factor of Saccharomyces cerevisiae was performed using short model peptides representing those sequences of the precursor protein, where cleavage is thought to occur in vivo. This search was done in a mutant lacking several of the unspecific vacuolar peptidases. The chromogenic peptide Cbz‐Tyr‐Lys‐Arg‐4‐nitroanilide led to the detection of a membrane‐bound enzyme called proteinase yscF. Cleavage of the synthetic peptide derivative occurs after the basic amino acid pair, a proposed signal for hormone processing. Optimum pH for the reaction is 7.2. The enzyme does not cleave after single basic amino acid residues indicating that it is distinct from trypsin‐like proteinases. Proteolytic activity is enhanced by Triton X‐100. The enzyme is strongly inhibited by EGTA, EDTA and mercurials but insensitive to phenylmethylsulfonyl fluoride. The enzyme activity is strongly dependent on Ca2+ ions. In a mutant (kex2), which accumulates an over‐glycosylated alpha‐factor precursor, no proteinase yscF activity can be found. Membrane‐bound peptidase activity possibly involved in removal of the arginyl and lysyl residues remaining at the carboxy terminus of the alpha‐factor pheromone peptide after the initial cut of the precursor molecule could be identified by using the model peptides Cbz‐Tyr‐Lys‐Arg and Cbz‐Tyr‐Lys.