Purification and Partial Characterization of Two Different Types of Proteinase Inhibitors (Inhibitors II-a and II-b) from Potatoes

Abstract

Two different proteins having powerful proteinase-inhibiting activity, referred to as inhibitors II-a and II-b, were isolated from potatoes (Solanum tuberosum) by the use of precipitation with ammonium sulfate, chromatography on carboxymethylcellulose, and filtration through Sephadex G-100. The final preparations appeared to be homogeneous on starch gel electrophoresis at pH 4.0 and 8.6. Both inhibitors inhibited bovine chymotrypsin (EC 3.4.4.5) and a bacterial proteinase, Nagarse, stoichiometrically. Inhibitor II-a also showed powerful stoichiometrical inhibition of bovine trypsin (EC 3.4.4.4), whereas inhibitor II-b gave very weak inhibition of the enzyme. Assuming one to one molecular reaction with proteinases, an average molecular weight of approximately 10, 000 was calculated for both inhibitors. The inhibitors were highly stable in the acidic pH range.