Characterization of a specific binding site for angiotensin II in chicken liver.
We have characterized a specific binding site for angiotensin II (AngII) in chicken liver membranes. Pseudo-equilibrium studies at 22 degrees C for 30 min have shown that this binding site recognizes AngII with a high affinity (pKD of 8.13 +/- 0.21). The binding sites are saturable and relatively abundant (maximal binding capacity varies from 0.318 to 0.88 pmol/mg of protein). Nonequilibrium kinetic analyses at 22 degrees C revealed a calculated kinetic pKD of 8.77 +/- 0.20. The binding site is pharmacologically distinct from the classic AngII receptors AT1 and AT2. Competitive binding studies with chicken liver membranes demonstrated the following rank order of effectiveness: AngII (human; Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) > AngI(Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu) > AngIII(Arg-Val-Tyr-Ile-His-Pro-Phe) > AngIV (Val-Tyr-Ile-His-Pro-Phe) > Ang(1-7) (Asp-Arg-Val-Tyr-Ile-His-Pro) > PD123319 (1-[4(dimethylamino)3-methylphenyl] methyl-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo [4,5-c]pyridine-6-carboxylic acid) > DuP753 (2-n-butyl-4-chloro-5 hydroxymethyl-1-[(2'-1H-tetrazol-5-yl)biphenyl-4-yl)methyl] imidazole. This atypical AngII binding site (chicken AT) was sensitive to increasing concentrations of DTT and Mn2+. The structure-activity relationship on position 1 of AngII showed that the primary N-terminal amine was essential for binding affinity ([Asp1]AngII > [Suc1]AngII > or = [Sar1]AngII), but modifications of the side chain in position 1 had less influence on the affinity ([Gly1]AngII > [Cys1]AngII approximately [aminoisobutyryl1]AngII approximately [Ser1]AngII > > > [Sar1]AngII). The presence of substantial quantities of this binding site in chicken liver membranes suggests the possibility that the chicken AT may play an important, yet unrecognized, role in the renin-angiotensin system.
Bouley
R
R
Department of Pharmacology, Faculty of Medicine, Université de Sherbrooke, QC, Canada.
Gosselin
M
M
Plante
H
H
Servant
G
G
Pérodin
J
J
Arcand
M
M
Guillemette
G
G
Escher
E
E
D000804:Angiotensin II / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism*; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002645:Chickens; D007457:Iodine Radioisotopes; D007700:Kinetics; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008566:Membranes / Q000378:metabolism; D011945:Receptors, Angiotensin / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D057911:Angiotensin Receptor Antagonists; D007457:Iodine Radioisotopes; D011945:Receptors, Angiotensin; D000804:Angiotensin II