[Purification and characterization of an extracellular protease from Staphylococcus aureus inhibited by EDTA].

A neutral protease, produced by Staphylococcus aureus, strain V8, was purified by precipitation with ammonium sulfate and acetone, and by chromatography on D.E.A.E.-cellulose. The purified protein is homogeneous by acrylamide gel electrophoresis. The molecular weight of the enzyme is estimated to be 28.000 daltons by gel filtration and 27.400 daltons by sedimentation equilibrium study. The amino acid composition indicates 251 residues and the absence of sulphydryl groups. Arginine is the NH2-terminal amino acid, while the COOH-terminal sequence of amino acids is Ala-Gly-Leu-Gl-Val. The protease exhibits a maximum proteolytic activity on casein at pH 7,0, and its activity is increased by 30 per cent on the addition of calcium ions. E.D.T.A. and E.G.T.A. completely inhibit the protease while the reagents of serine enzymes are without effect. This enzyme, which contains mainly calcium in its molecule, hydrolyses the peptide bonds, of the insulin B-chain, in which the amino groups of hydrophobic amino acids are involved. Unlike the other metalloproteases, no hydrolysis is observed for the peptide bond Phe(24)-Phe(25) while the peptide bond Phe(1)-Val(2) is attacked.