Activation and regeneration of rhodopsin in the insect visual cycle.
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.
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
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Kiselev
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Subramaniam
D000818:Animals; D000941:Antigens / Q000378:metabolism*; D019393:Arrestin; D003624:Darkness; D004330:Drosophila; D005136:Eye Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008027:Light; D008954:Models, Biological; D010766:Phosphorylation; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism*; D012243:Rhodopsin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
D000941:Antigens; D019393:Arrestin; D005136:Eye Proteins; C013110:metarhodopsins; D012243:Rhodopsin; D019204:GTP-Binding Proteins