Somatostatin competes with the central portion of gastrin releasing peptide for binding to a 120 kDa protein.
[(125)I]Gastrin releasing peptide (GRP) and [(125)I]somatostatin were cross-linked with bis(sulfosuccinimidyl)suberate to a 120 kDa membrane protein in Triton extracts of different cell types. Labeling of the 120 kDa protein was blocked (IC(50) ? 10(?8) M) by unlabeled GRP, GRP(14-27) and somatostatin but not by 100 nM bombesin, [Tyr(4)]bombesin, AcGRP(20-27), three biologically active somatostatin analogs or peptides unrelated to GRP or somatostatin. Binding involves a tripeptide sequence consisting of aryl, nonpolar and positively charged moieties in residues 7-9 (Phe-Trp-Lys) of the receptor binding site of somatostatin and residues 15-17 (Tyr-Pro-Arg) of GRP, a region distinct from its biologically active carboxyl-terminus.
Fanger
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Merrell Dow Research Institute, 2110 East Galbraith Road, Cincinnati, OH 45215, U.S.A.
Wade
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