Specificities of extracellular and ribosomal serine proteinases from Bacillus natto, a food microorganism

Abstract

The specificities of extracellular and ribosomal serine proteinase from Bacillus natto, a food microorganism, were investigated. Both proteins have highly restricted and characteristic specificities. With the extracellular serine proteinase, initial cleavage site was observed at Leu 15-Tyr 16, secondary site at Ser 9-His 10 and additional cleavage sites at Gln 4-His 5 and His 5-Leu 6 in the oxidized insulin B-chain. Hydrolysis of proangiotensin with the extracellular serine proteinase was observed primarily at Phe 8-His 9 and secondary at Tyr 4-Ile 5. The extracellular serine proteinase has a K m of 0.08 mM and k cat of 3 s −1 for angiotensin hydrolysis. With the ribosomal proteinase, initial cleavage site of the oxidized insulin B-chain was observed at Leu 15-Tyr 16 and additional cleavage site at Phe 24-Phe 25. Hydrolysis of proangiotensin was observed at Tyr 4-Ile 5 bond with the ribosomal proteinase.