[Isolation of proteinase I from E. coli cells using affinty chromatography on bacitracin-Sepharose]

A serine proteinase (proteinase I) was isolated in a homogeneous state from E. coli K12 cells, using bacitracin-Sepharose 4B affinity chromatography. The enzyme effectively cleaved N alpha-acetyl-L-phenylalanine beta-naphthyl ester. The proteinase was inhibited by diisopropylphosphofluoridate and phenylmethanesulphonyl fluoride, but was resistant to EDTA and natural trypsin or subtilisin protein inhibitors. The enzyme did not cleave trypsin and subtilisin synthetic substrates, possessing a narrow substrate specificity. The amino acid composition of the enzyme was determined. The enzyme molecular weight was found to be about 20 000.