Photoaffinity labeling of a peptide secretagogue receptor in the exocrine pancreas
Galardy, R.E.; Jamieson, J.D.
Molecular Pharmacology 13(5): 852-863
1977
ISSN/ISBN: 0026-895X PMID: 197395 Document Number: 111116
The photoaffinity label 2-nitro-5-azidobenzoyl-Gly-Trp-Met-Asp-Phe-NH2 (NAB-CCK-5) mimics cholecystokinin and the more potent secretagogue cerulein in stimulating discharge of exportable proteins from acinar cells of the guinea pig pancreas in vitro. Photolysis of this affinity label in the presence of pancreatic lobules (small clusters of acini) causes irreversible stimulation of protein discharge which is indistinguishable in rate, magnitude and morphological aspects from that observed with the most potent doses of cerulein. The irreversible agonist activity cannot be removed by extensive washing of the lobules and is blocked only by metabolic inhibition. Irreversible agonist activity is not observed without photolysis, nor is it observed after photolysis of lobules in the presence of 2-nitro-5-azidobenzoic acid, 2-nitro-5-azidobenzoyl-angiotensin II, 2-nitro-5-azidobenzoyl-Gly-Gly-Met-Asp-Phe-NH2, cerulein or with previously photolyzed NAB-CCK-5. Protection by native peptide secretagogues against irreversible labeling by NAB-CCK-5 could not be demonstrated. Although the biologically active sites which were labeled appear to be those responsible for peptide secretagogue-mediated release of exportable proteins, the absence of competition by native secretagogues for labeling shows that the mechanism of labeling NAB-CCK-5 is not understood.