Purification and properties of serine protease from Halobacterium halobium

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Abstract
Pure extracellular serine protease was isolated from the culture filtrate of H. halobium by bacitracin-Sepharose affinity chromatography. The enzyme activity was completely and irreversibly lost if the NaCl concentration fell below 2 M. The protease consists of 1 polypeptide chain with a MW of 41,000. It is characteristically enriched in Asx and Glx content, whereas the level of basic amino acids in the enzyme molecule is unusually low. The protease shows a preference for leucine in the carboxylic side of the scissile bond of the substrate, cleaving the B-chain of oxidized bovine insulin only at the Leu15-Tyr16 bond and liberating p-nitroaniline from L-pyroglutamyl-L-alanyl-L-alanyl-L-leucine-p-nitroanilide.