title: Light-induced GTPase activity and GTP[gamma S] binding in squid retinal photoreceptors.
abstract: Illumination greatly increases the GTPase activity in homogenates of squid (Loligo) whole retinas or rhabdomeric membranes. Adenylylimidodiphosphate inhibits the light-insensitive (but not the light-sensitive) GTPase activity in these homogenates. Illumination also greatly increases the binding of GTP[gamma S] to the rhabdomeric membranes. This binding at saturating illuminations indicates that there are approximately 10-100 times more rhodopsin molecules than G-protein molecules in squid photoreceptors. Each light-activated rhodopsin molecule activates about 10 G-protein molecules which might provide amplification for the first stage of the phototransduction cascade.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Washington University, St. Louis.
authors.forename: J E
authors.initials: JE
authors.lastname: Brown
authors.forename: A
authors.initials: A
authors.lastname: Combs
authors.forename: K
authors.initials: K
authors.lastname: Ackermann
authors.forename: C C
authors.initials: CC
authors.lastname: Malbon
mesh_terms: D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D003623:Dark Adaptation; D049832:Decapodiformes; D020558:GTP Phosphohydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism*; D008027:Light; D010786:Photoreceptor Cells / Q000737:chemistry / Q000201:enzymology*; D012243:Rhodopsin / Q000032:analysis; D015398:Signal Transduction
chemical_list: D000266:Adenylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D012243:Rhodopsin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins