Metabolism of gastrin and cholecystokinin by endopeptidase 24.11 from the pig stomach

The purpose of this investigation is to examine the metabolism and inactivation of human and porcine gastrin 17 (nonsulfated) (G-17) and cholecystokinin octapeptide (sulfated) (CCK-8) by gastric endopeptidase 24.11. Endopeptidase 24.11 was isolated by immunoaffinity chromatography using a monoclonal antibody to the kidney enzyme. Peptides were incubated with endopeptidase 24.11. The digests were either fractionated by reverse-phase high-pressure liquid chromatography and the products identified by amino acid analysis or they were used for bioassays. Digests of human gastrin were assayed for stimulation of acid secretion in the anesthetized rat, and cholecystokinin digests were assayed for the stimulation of amylase secretion from isolated rat pancreatic acini. Human G-17 was degraded by cleavage of the Trp⁴-Leu⁵-,Ala¹¹-Tyr¹²,Gly¹³-Trp¹⁴,Trp¹⁴-Met¹⁵, and Asp¹⁶-Phe¹⁷-NH₂ bonds, and the fragments (1-16), (1-13), (1-11), (1-4), (5-11), (5-13), (12-13), (12-14), (14-16), and (17-NH₂) were identified. Porcine G-17 was degraded by hydrolysis of the Ala¹¹-Tyr¹²,Gly¹³-Trp¹⁴, and Asp¹⁶-Phe¹⁷-NH₂ bonds producing (1-16), (1-13), (1-11), (12-13), (14-16), and (17-NH₂) fragments. CCK-8 was degraded by hydrolysis of the Gly⁴-Trp⁵ and Asp⁷-Phe⁸-NH₂ bonds, and the fragments (1-7), (1-4), (5-7), (5-8), and (8-NH₂) were identified. There was a progressive decline in the biological activity with incubation time.