A novel extracellular subtilisin inhibitor produced by a Streptomyces sp

The amino acid composition and inhibitory properties of a protein (SI-1-72) isolated from the culture medium of a Streptomyces sp. have been investigated. SI-1-72 appears to be a monomer protein of molecular mass about 13,100 Da and amino acid composition which differs from that of the inhibitors of the Streptomyces subtilisin inhibitor (SSI) family. Furthermore, it was found to exhibit novel specificity: strong inhibitory effect against microbial alkaline proteinases, moderate effect towards chymotrypsin and elastase, and no inhibition of the other serine proteinases, as well as of the cysteine, aspartate and metallo-proteinases.