The KEX2 gene-encoded, membrane-bound Ca2+-dependent thiol endoproteinase, proteinase yscF, responsible for processing of the precursor protein of the sex pheromone α-factor of the yeast Saccharomyces cerevisiae was solubilized from the membraneous fraction and partially purified. Gel filtration revealed an apparent Mr of the native protein of around 150 000. Ca2+ concentration for half-maximal activity was in the micromolar range and concentration of the substrate Cbz-Tyr-Lys-Arg-4-nitroanilide for half-maximal velocity was 0.05 mM. The enzyme is able to cleave basic amino acids from the carboxy-terminus of peptides and probably involved in final maturation of the α-factor peptides generated by proteinase yscF is membrane-associated, active at neutral pH and responds strongly to the serine proteinase inhibitor phenylmethylsulfonyl fluoride as well as to -SH group blocking agents.
