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Activation and Regeneration of Rhodopsin in the Insect Visual Cycle

1994; American Association for the Advancement of Science; Volume: 266; Issue: 5189 Linguagem: Inglês

10.1126/science.7973725

1095-9203

Alexander Kiselev, Sriram Subramaniam,

Neuroscience and Neuropharmacology Research

Light absorption by rhodopsin generates metarhodopsin, which activates heterotrimeric guanine nucleotide-binding proteins (G proteins) in photoreceptor cells of vertebrates and invertebrates. In contrast to vertebrate metarhodopsins, most invertebrate metarhodopsins are thermally stable and regenerate rhodopsin by absorption of a second photon. In experiments with Rh1 Drosophila rhodopsin, the thermal stability of metarhodopsin was found not to be an intrinsic property of the visual pigment but a consequence of its interaction with arrestin (49 kilodaltons). The stabilization of metarhodopsin resulted in a large decrease in the efficiency of G protein activation. Light absorption by thermally stable metarhodopsin initially regenerated an inactive rhodopsin-like intermediate, which was subsequently converted in the dark to active rhodopsin. The accumulation of inactive rhodopsin at higher light levels may represent a mechanism for gain regulation in the insect visual cycle.