title: Unexpected binding of an octapeptide to the angiotensin II receptor.
abstract: An octapeptide, TBI-22 (Lys-Gly-Val-Tyr-Ile-His-Ala-Leu), inhibited binding of angiotensin II by a solubilized angiotensin receptor partially purified from rabbit liver. This inhibition appears to result from competition for binding to the same receptor. Radioiodinated TBI-22, like angiotensin II, bound to the solubilized receptor with an affinity such that the binding was inhibited 50% by unlabeled TBI-22 or angiotensin II at nanomolar concentrations. The binding reaction, like that for angiotensin II, required p-chloromercuriphenylsulfonic acid and was reversed in the presence of dithiothreitol. TBI-22 and angiotensin II share the sequence Val-Tyr-Ile-His; this tetrapeptide alone, however, did not inhibit binding of angiotensin II. Replacement of the tyrosine residue by aspartic acid in TBI-22 greatly reduced the ability of the peptide to compete with angiotensin II for binding, suggesting an important contribution of this residue to the configuration required for recognition by the receptor.
mesh_terms: D000595:Amino Acid Sequence; D000804:Angiotensin II / Q000276:immunology / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D009842:Oligopeptides / Q000378:metabolism*; D011817:Rabbits; D011945:Receptors, Angiotensin / Q000276:immunology / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D009842:Oligopeptides; D011945:Receptors, Angiotensin; D000804:Angiotensin II