Thermodynamic analysis of agonist and antagonist binding to membrane-bound and solubilized A1 adenosine receptors.
The thermodynamic properties of the agonist [Adenine-2,8-3H, ethyl-2(3)-H]-N6-phenylisopropyladenosine ([3H]R-PIA) and the antagonist 8-Cyclopentyl-1,3-[3H]dipropylxanthine ([3H]DPCPX) binding to membrane-bound and 3-3[-(choloamidopropyl)-dimethylammoniol-1-propanesulfonate/ digitonin- solubilized A1 adenosine receptors from pig brain cortex were evaluated. Rate constants for [3H]R-PIA and [3H]DPCPX association (k+1) and dissociation (k-1) processes to this receptor subtype were measured from association-dissociation experiments at six different temperatures. The values for equilibrium association constant (KA = 1/KD) were derived from rate constant values (k+1/k-1). The antagonist binding to membrane-bound receptors, the agonist binding to fast kinetic component membrane-bound receptors and the agonist binding to soluble receptors showed a linear temperature-dependence of the standard free-energy change. The first two processes are enthalpy- and entropy-driven, and the third process is enthalpy-driven with entropy working against it. On the other hand, a curvilinear temperature-dependence appears in the agonist binding to slow kinetic component membrane-bound receptors and in the antagonist binding to soluble receptors, but analyzing the semireactions (association-dissociation) involved in each case reveals that the thermodynamic behavior is very different. The thermodynamic similarities and differences are discussed in terms of receptor--G protein interaction.
Departament de Bioquímica i Fisiologia, Facultat de Química, Universitat de Barcelona, Catalonia, Spain.
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Casadó
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Allende
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Mallol
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Franco
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Lluis
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Canela
D000818:Animals; D007700:Kinetics; D008566:Membranes / Q000378:metabolism / Q000648:ultrastructure; D010660:Phenylisopropyladenosine / Q000737:chemistry* / Q000378:metabolism*; D004856:Postural Balance; D011983:Receptors, Purinergic / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D012996:Solutions; D013552:Swine; D013696:Temperature; D013816:Thermodynamics; D014316:Tritium; D014970:Xanthines / Q000737:chemistry* / Q000378:metabolism*
D011983:Receptors, Purinergic; D012996:Solutions; D014970:Xanthines; D014316:Tritium; D010660:Phenylisopropyladenosine; C051360:1,3-dipropyl-8-cyclopentylxanthine