Binding stoichiometry of a fluorescent cGMP analogue to membranes of retinal rod outer segments.
The high-affinity binding of the cGMP analogue 8-(5-thioacetamidofluorescein)-cGMP to rod outer segment membranes depleted of peripherally bound proteins has been defined by equilibrium dialysis (mean +/- SD): membranes contain about one cGMP binding site per 130 rhodopsin molecules; the concentration of free ligand for half saturation is 2.0 +/- 0.6 microM; the apparent Hill coefficient of the bound versus free ligand relationship is 1.7 +/- 0.5; half saturation of the binding sites is sufficient for 85% activation of calcium permeability. A gating mechanism is proposed.
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism; D003956:Dialysis; D005452:Fluoresceins; D005456:Fluorescent Dyes / Q000138:chemical synthesis; D066298:In Vitro Techniques; D008024:Ligands; D008566:Membranes / Q000378:metabolism; D010786:Photoreceptor Cells / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D005452:Fluoresceins; D005456:Fluorescent Dyes; D008024:Ligands; C049144:8-(5-thioacetamidofluorescein)cyclic-GMP; D006152:Cyclic GMP