Kiselev A, Subramaniam S
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Science. 1994 Nov 25;266(5189):1369-73. doi: 10.1126/science.7973725.
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.
视紫红质吸收光会产生变视紫红质，变视紫红质可激活脊椎动物和无脊椎动物光感受器细胞中的异三聚体鸟嘌呤核苷酸结合蛋白（G蛋白）。与脊椎动物的变视紫红质不同，大多数无脊椎动物的变视紫红质具有热稳定性，并通过吸收第二个光子再生视紫红质。在用果蝇Rh1视紫红质进行的实验中，发现变视紫红质的热稳定性并非视觉色素的固有特性，而是其与抑制蛋白（49千道尔顿）相互作用的结果。变视紫红质的稳定导致G蛋白激活效率大幅降低。热稳定的变视紫红质吸收光最初会再生一种无活性的视紫红质样中间体，该中间体随后在黑暗中转化为活性视紫红质。在较高光照水平下无活性视紫红质的积累可能代表昆虫视觉循环中增益调节的一种机制。
