Purification and Properties of a Carboxypeptidase Inhibitor from Potatoes

Abstract

Abstract An inhibitor of the pancreatic carboxypeptidase A and B (Ryan, C. A. (1971) Biochem. Biophys. Res. Commun. 44, 1265–1270) has been purified from Russet Burbank potatoes. The inhibitor is a polypeptide having a molecular weight of approximately 3100, as estimated by gel filtration, and contains 37 to 39 amino acid residues. The amino group of the NH2-terminal residue is blocked and the COOH-terminal residue is apparently glycine. The presence of 6 halfcystine residues per molecule and absence of free thiols indicate that the inhibitor possesses three disulfide bonds. The Ki values for the inhibition of the peptidase activities of bovine carboxypeptidase A and porcine carboxypeptidase B were estimated to be 5 x 10-9 m and 5 x 10-8 m, respectively.