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

Abstract

Potato proteinase inhibitors II-a and II-b were characterized in terms of their major chemical and physicochemical properties. The molecular weights were determined to be approximately 10,500 for both inhibitors. The inhibitors possess one polypeptide chain as judged from terminal amino acid analyses (1 mole of amino-terminal alanine and 1 mole of carboxyl-terminal alanine in both inhibitors). Further, the amino acid compositions' of the inhibitors were found to be closely related each other. Noteworthy are the comparatively high contents of cystine and glycine, and the lack of methionine and tryptophan in both inhibitors. The isoelectric points were found to be at approximately pH 8.5 for inhibitor II-a and pH 9.1 for inhibitor II-b, respectively. Both inhibitors were completely inactivated by the modification of free amino groups in the molecules with trinitrobenzenesulfonic acid.