Active carboxypeptidase B is present in free form in serum from patients with acute pancreatitis

Background: Active carboxypeptidase B (aCAP) is the main product of activation of procarboxypeptidase. The other product derived from procarboxypeptidase B (proCAP), the activation peptide carboxypeptidase B (CAPAP), has been shown to be a marker for severity in acute pancreatitis. There have been relatively few studies dealing with the role of this enzyme in acute pancreatitis. Methods: A double-antibody ELISA for immunoreactive aCAP (ir-aCAP) was developed, and ir-aCAP was determined in the serum of patients with acute pancreatitis and characterized using gel filtration. Results: Serum from healthy individuals contained minimal levels of ir-aCAP, while serum from 25 patients with acute pancreatitis contained between 0.6 and 158 nmol/l. Gel filtration of serum samples from patients with acute pancreatitis showed the presence of two peaks of ir-aCAP, one corresponding to the molecular size of the free active enzyme and one corresponding to cross-reactive pro-CAP. When pure aCAP was mixed with serum in vitro, all ir-aCAP was recovered as one peak of free enzyme. No immunoreactivity disappeared or changed in molecular size, as might be expected if the active enzyme was bound to an inhibitor. Conclusion: aCAP is present in free form in the circulation of patients with acute pancreatitis.