title: A light-stimulated increase of cyclic GMP in squid photoreceptors.
abstract: Photoreceptor outer segments isolated from squid retina are known to contain a light-activated GTP-binding protein. Here it is shown that these photoreceptors contain around 0.01 mol cyclic GMP per mol rhodopsin. Adding GTP in the dark stimulates the production of 0.0003-0.001 mol cyclic GMP/mol rhodopsin per min. GTP and light cause a 2-fold faster increase in cyclic GMP. These results show that either (1) squid rhodopsin activates a guanylate cyclase, or (2) there is a constant guanylate cyclase activity and photoexcited rhodopsin inhibits a cyclic GMP phosphodiesterase.
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D049832:Decapodiformes / Q000378:metabolism*; D008027:Light; D008871:Microvilli / Q000378:metabolism; D010786:Photoreceptor Cells / Q000378:metabolism* / Q000528:radiation effects; D012243:Rhodopsin / Q000378:metabolism; D012374:Rod Cell Outer Segment / Q000378:metabolism
chemical_list: D012243:Rhodopsin; D000242:Cyclic AMP; D006152:Cyclic GMP