Phosphorylation of rhodopsin as a possible mechanism of adaptation

Light-induced phosphorylation of rhodopsin has been extensively studied by a number of investigators from a biochemical point of view. However, little is known about the physiological function of this reaction. The slow rates measured for phosphorylation and dephosphorylation suggest that it may be involved in visual adaptation rather than in excitation. This paper presents biochemical data obtained from phosphorylation experiments in isolated photoreceptor membranes as well as in the more physiological system of whole retinas and living animals. An attempt is made to compare the phosphorylation reaction with visual adaptation hypotheses taken from the electrophysiological literature. Finally, effects of cyclic nucleotide metabolism on the sensitivity of photoreceptors are presented and discussed.Abbreviations used ATP adenosine 5-triphosphate - GTP guanosine 5-triphosphate - ROS rod outer segments - IBMX isobutylmethylxanthine - cyclic GMP guanosine 3, 5-monophosphatePresented at the EMBO-Workshop on Transduction Mechanism of Photoreceptors, Jülich, Germany, October 4–8, 1976