A membrane-bound, calcium-dependent protease in yeast alpha-cell cleaving on the carboxyl side of paired basic residues.

Paired basic residues are known as a typical site for proteolytic processing of precursors of bioactive peptides. By using a fluorogenic substrate Boc-Gln-Arg-Arg-MCA, a unique endoprotease exhibiting hydrolytic specificity toward the carboxyl side of paired basic residues was partially purified (about 4600-fold) from the membrane fraction of yeast Saccharomyces cerevisiae alpha-cells. The enzyme is a calcium-dependent thiol protease, with optimal pH at 7.0. It is a glycoprotein, with an apparent molecular weight of about 100,000-120,000. It cleaves fluorogenic substrates and a synthetic model peptide at the carboxyl side of paired basic residues. From its unique substrate specificity, this enzyme may be involved in precursor processing in vivo.