1. Light-induced GTPase activity and GTP[gamma S] binding in squid retinal photoreceptors
- Author
-
Karen E. Ackermann, Joel E. Brown, Anthony Combs, and Craig C. Malbon
- Subjects
Rhodopsin ,GTP' ,Light ,Physiology ,Adenylyl Imidodiphosphate ,Dark Adaptation ,GTPase ,GTP Phosphohydrolases ,GTP-Binding Proteins ,biology.animal ,Animals ,Photoreceptor Cells ,Squid ,biology ,Chemistry ,Decapodiformes ,Anatomy ,Sensory Systems ,Membrane ,Retinal Photoreceptors ,Guanosine 5'-O-(3-Thiotriphosphate) ,biology.protein ,Biophysics ,Light induced ,Visual phototransduction ,Signal Transduction - 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[γS] 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.
- Published
- 1991