Isolation of a Low Molecular Weight Active Fragment of Potato Proteinase Inhibitor IIb

Abstract

A low molecular weight active fragment of potato proteinase inhibitor IIb was obtained by incubating the inhibitor with an equimolar amount of trypsin [EC 3. 4. 21. 4] at pH 8 and 30° for 16hr, followed by gel filtration through Sephadex G-50, treatment with trichloroacetic acid, and CM-cellulose chromatography. The purified active fragment consisted of a single peptide chain with a molecular weight of 4, 300, comprising 39 amino acid residues. It retained very strong inhibitory activity against chymotrypsin [EC 3. 4. 21. 1] and subtilisin [EC 3. 4. 21. 14]. However, the yield of this active fragment was rather low and was variable. On further incubation with trvpsin, it was converted into smaller inactive peptides.