Preparation and characterization of a probe for the cholecystokinin octapeptide receptor, N/sup α/ (125I-desaminotyrosyl)CCK-8, and its interactions with pancreatic acini

A biologically active, high specific activity (2000 Ci/mmol), radiolabeled derivative of cholecystokinin octapeptide (CCK-8) was synthesized, purified, characterized, and used to investigate interactions between CCK-8 and its receptor on rat pancreatic acini. N/sup α/(125I-desaminotyrosyl)CCK-8 was prepared by acylation of CCK-8 with 125I-labeled N-hydroxysuccinimidyl 3-(4-hydroxyphenyl)propionate in dimethylformamide and triethylamine. It was purified by cation exchange chromatography (sulfopropyl-Sephadex), followed by either gel filtration on Sephadex G-25 or high performance liquid chromatography on a reversed-phase C-18 column. Its nonradioactive analogue, N/sup α/(125I-desaminotyrosyl)CCK-8 to pancreatic acini was rapid, reversible, temperature-dependent, saturable, and specific. This binding was inhibited by each molecular species of cholecystokinin, but not by structurally unrelated ligands. Good correlation existed between potencies of the species of cholecystokinin for inhibiting binding of this receptor probe and for stimulating pancreatic secretion. N/sup α/(125I-desaminotyrosyl) CCK-8 binding was inhibited by its nonradioactive analogue, N/sup α/(127I-desaminotyrosyl)CCK-8, in a manner identical with that by iodinated desaminotyrosyl moiety to the NH2-terminal end of CCK-8 does not compromise the ability of this peptide to either bind to its pancreatic receptor or stimulate a biologic response