A NOVEL PROTEINACEOUS KEX-2 PROTEINASE-INHIBITOR, KEXSTATIN, FROM STREPTOMYCES-PLATENSIS Q268

We found a novel proteinaceous Kex 2 proteinase inhibitor, named kexst atin, in the culture supernatant of Streptomyces platensis Q268. The p urified kexstatin was homogeneous by SDS-PAGE and the molecular weight was estimated to be 13,000. The N-terminal amino acid sequence of kex statin has high similarity to Streptomyces subtilisin inhibitor (SSI), suggesting that kexstatin belongs to the SSI family. Kexstatin was a strong inhibitor of Kex 2 proteinase and subtilisin but not thermolysi n, trypsin, or chymotrypsin. The IC50 value of kexstatin against 1 mu g of Kex 2 proteinase was 1.4 mu g.