[A serine proteinase from Thermoactinomyces vulgaris, strain INMI-4a]

A serine proteinase was isolated from the cultural filtrate of the thermophylic actinomycet Thermoactinomycet vulgaris, strain INMI-4a. The purification procedure included affinity chromatography on bacitracin-Sepharose, ion-exchange separation on aminosilochrome, and gel-filtration on Sephadex G-25, resulting in a 194-fold purification and the 55% yield of the enzyme. The molecular weight of the enzyme as determined by polyacrylamide gel electrophoresis in the presence of Na-SDS as well as by gel-filtration on Sephadex G-75 is equal to 28 000; the amino acid composition is: Lys11, His4, Arg5, Asp33, Thr22, Ser24, Glu16, Pro16, Gly30, Ala38, Cys1-2, Val20, Met1, Ile14, Leu8, Tyr16, The4, Trp6-7. The isoelectric point lies at pH 8--9; the pH optimum for the peptide substrate hydrolysis is Z-L-Ala-L-Ala-L-Leu-pNA is at 8.2. The enzyme is stable at pH 7--9. The temperature optimum of the proteolytic activity lies at 55 degrees; however, the enzyme is stable to heating for 1 h at 37 degrees. The proteinase is completely inactivated by the serine proteinase specific inhibitors--phenylmethylsulphofluoride and the protein inhibitor IT-AjT from Actinomyces, as well as by p-chloromercuribenzoate. The enzyme shows lytic activity against the cells of E. coli, Micrococcus lysodeicticus and of the yeasts. The Thermoactinomyces vulgaris serine proteinase, being definitely different from the serine proteinases from Actinomyces griseus, also reveals specific differences when compared to bacterial serine proteinases, e. g. subtilisins. There are some indications to the enzyme relationship with the family of carboxypeptidase Y-like serine proteinases.