Isolation and characterization of the carboxypeptidase Y inhibitor from yeast

Rapid acetone fractionation of crude yeast extract at low temperature separates carboxypeptidase Y inhibitor from the carboxypeptidase Y-inhibitor complex. On a protein basis the inhibitor has been purified 890-fold, resulting in homogeneity as determined by disc electrophoresis and filtration on Sephadex G-75. The molecular weight was calculated to be about 25,000. The inhibitor is heat-labile in crude extracts, whereas in the purified form it loses only 11% of its activity when it is heated at 100 degrees for 5 min. The inhibitor is inactivated by the yeast proteinases A (EC 3.4.23.8) and B (EC 3.4.22.9), respectively, but not by carboxypeptidase Y (EC 3.4.12.8). The inhibitor inhibits carboxypeptidase Y at a 1.5:1.0 protein-based weight ratio by 80%. At the same concentration ratios, proteinases A and B from yeast, as well as bovine pancreas carboxypeptidases A and B, are not inhibited.