Heat stable proteinase from Thermomonospora fusca Characterization as a serine proteinase

An extracellular proteinase secreted by the thermophilic bacteria Thermomonospora fusca YX (YX‐proteinase) is a serine proteinase as shown by its inactivation by the site specific reagents, phenylmethanesulfonyl fluoride, dansyl fluoride, and carbobenzoxy‐l‐phenylalanine chloromethyl ketone. This conclusion is further supported by the effect of various proteinase inhibitors on its activity. The activity of the proteinase toward small synthetic ester substrates shows that the enzyme has a primary specificity for the aromatic and hydrophobic amino acids. The amino acid composition and NH₂ ‐terminal sequence, as well as its size, suggest that the enzyme is related to the chymotrypsin‐like microbial proteinase, α‐lytic protease from Myxobacter 495 and protease A and B from Streptomyces griseus.