SECRETED SERINE-PROTEASE FROM THE SPORE-FORMING BACTERIUM BACILLUS-INTERMEDIUS-3-19

Extracellular alkaline serine protease was purified to homogeneity by chromatography on bacitracin-Sepharose from the culture liquid of B. i ntermedius. The enzyme was tested for substrate specificity using natu ral and synthetic peptides. The enzyme displayed maximal activities to ward tripeptide substrates and preferentially hydrolyzed leucine and p henylalanine p-nitroanilides. The enzyme was completely inhibited by d iisopropyl fluorophosphate and partially suppressed by thiol reagents, suggesting that it pertains to subtilisin-like thiol-dependent serine proteases; The amino acid composition of the enzyme was determined. I t contained one to three semicystine residues, one of which could prob ably be cysteine. The N-terminal amino acid sequence of the enzyme AQT VPYGIPQIKAPA displays a 80% homology to subtilisin Carlsberg and BPN'.