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Science 25 November 1994:
Vol. 266. no. 5189, pp. 1369 - 1373
DOI: 10.1126/science.7973725
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Articles

Science, Vol 266, Issue 5189, 1369-1373
Copyright © 1994 by American Association for the Advancement of Science

articles

Activation and regeneration of rhodopsin in the insect visual cycle

A Kiselev and S Subramaniam

Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205.

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.


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