Human serum procarboxypeptidase A

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Abstract
Zymogen activation is an important biochemical control process and has important physiological and pathological implications. Procarboxypeptidase A, the enzyme precursor, and carboxypeptidase A, its active product, were simultaneously measured in serum by using an affinity resin and the synthetic peptide substrate N-(2-furanacryloyl)-L-phenylalanyl-L-phenylalanine. Serum procarboxypeptidase A is activated by trypsin, chymotrypsin, plasmin, subtilisin or urokinase but not by thrombin or enteropeptidase. The MW of the precursor is .apprx. 5000-10,000 greater than that of the active product. Both enzymes and precursor increase in serum in the course of pancreatic inflammation, but the degree of activation can vary up to 2000-fold, independent of the amount of precursor present. The existence of this pancreatic proteolytic precursor in serum opens new avenues for the invesigation of zymogen activation and its regulation.