Specificity of the carboxypeptidase inhibitor from potatoes

Carboxypeptidases from animal, plant, fungal, and bacterial sources were tested for their ability to bind to the carboxypeptidase inhibitor from Russet Burbank potatoes. Enzymes which participate in the degradation of dietary protein were partially purified from animal species as diverse as the cow and the limpet, and all were potently affected by the inhibitor. However, several zymogens of the enzymes in this group were tested and shown not to bind immobilized inhibitor. With the exception of an enzyme from mast cells and a novel carboxypeptidase A-like enzyme from bovine placenta, all animal carboxypeptidases which were not of digestive tract origin were not affected by the inhibitor. The inhibitor had no effect on the enzymic activities of all plant and most microbial carboxypeptidases. However, a strong association between the inhibitor and Streptomyces griseus carboxypeptidase has been noted previously and a low affinity (K(i) about 10 micromolar) for a carboxypeptidase G(1) from an acinetobacterium was found in this study.