Thermitase, a thermostable serine protease from Thermoactinomyces vulgaris. Classification as a subtilisin-type protease

Studies on the amino acid composition, chemical modifications, and characterization of the cyanogen bromide cleavage peptides of a thermostable serine protase (thermitase) from Thermoactinomyces vulgaris were performed. The amino acid analysis shows that the enzyme contains a single cysteine and methionine residue. From the amino acid composition as well as a partial sequence determination around the single methionine residue it is concluded that thermitase belongs to the subtilisin-type proteases. The two peptides obtained by cyanogen bromide cleavage were further characterized by amino acid analysis and molecular weight determination yielding 25 000 and 6 000 daltons, respectively. Chemical modification experiments show that in addition to the active site serine and histidine residue the cysteine as well as the methionine residue are essential for activity of the enzyme. The alignment of these amino acids in the polypeptide chain of the thermitase is supposed.