title: A monoclonal antibody to guanine nucleotide binding protein inhibits the light-activated cyclic GMP pathway in frog rod outer segments.
abstract: A monoclonal antibody that blocks the light-activated cyclic GMP (cGMP) pathway in frog photoreceptor outer segments (ROS) has been obtained. The antibody (4A) inhibits guanine nucleotide binding to G-protein, the intermediate that links rhodopsin excitation to cGMP phosphodiesterase (PDE), inhibiting light-induced PDE activity as a consequence. Antibody inhibition of the light-activated cGMP pathway is complete at a stoichiometry of approximately one antibody per G-protein in the mixture, which indicates high specificity of the inhibition. Inhibition is more pronounced than that caused by PDE inhibitors such as isobutylmethylxanthine (IBMX) or Ro 20-1724. Antibody 4A has the further effect of inhibiting the phosphorylation of two low molecular weight proteins, components I and II, whose phosphorylation normally can be stimulated by raising cGMP levels. The inhibition is not overridden by adding cGMP, which suggests that the G-protein influences these phosphorylations by a pathway distinct from its action on cGMP concentration. Antibody 4A may prove useful as a probe of the relevance of the cGMP pathway to visual transduction in living photoreceptors. Six other monoclonal antibodies to G-protein, as well as six monoclonal antibodies to rhodopsin and one to PDE, do not block light-activated guanine nucleotide binding, PDE activity, or ROS protein phosphorylations.
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000502:physiology*; D006152:Cyclic GMP / Q000502:physiology*; D005136:Eye Proteins / Q000276:immunology / Q000502:physiology; D019204:GTP-Binding Proteins / Q000276:immunology*; D020962:Heterotrimeric GTP-Binding Proteins; D008027:Light; D010766:Phosphorylation; D010786:Photoreceptor Cells / Q000276:immunology / Q000502:physiology*; D011892:Rana catesbeiana; D012374:Rod Cell Outer Segment / Q000276:immunology / Q000502:physiology*; D015293:Transducin
chemical_list: D000911:Antibodies, Monoclonal; D005136:Eye Proteins; C034809:GNAT1 protein, human; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D019204:GTP-Binding Proteins; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin; D006152:Cyclic GMP