COUPLING OF PHOTOEXCITED RHODOPSIN TO INOSITOL PHOSPHOLIPID HYDROLYSIS IN FLY PHOTORECEPTORS
COUPLING OF PHOTOEXCITED RHODOPSIN TO INOSITOL PHOSPHOLIPID HYDROLYSIS IN FLY PHOTORECEPTORS
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DOI：
10.1073/pnas.84.19.6939
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发表时间：
1987-10-01
影响因子：
11.1
通讯作者：
SELINGER, Z
中科院分区：
文献类型：
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作者：
DEVARY, O;HEICHAL, O;SELINGER, Z
苍蝇感光膜用于测试光和引起感光器兴奋的化合物对限定的生化反应的影响。补充电生理学研究检查是否假定的第二信使兴奋苍蝇感光细胞。该分析揭示了以下事件顺序：光激发视紫红质通过促进GTP结合来激活G蛋白。然后G蛋白激活磷脂酶G，产生三磷酸肌醇，这反过来又作为一个内部信使，使感光细胞去极化。GTP类似物的结合测定和GTdR活性的测量表明，每个感光细胞有160万个G蛋白拷贝。GTP结合组分是41-kDa的蛋白质，并且光激活的GTP依赖于视紫红质到变视紫红质的光转化。磷脂酶C活性的分析表明，这种酶是G蛋白的严格控制下，形成的主要产品是肌醇三磷酸，该产品是快速水解的特定磷酸单酯酶。将三磷酸肌醇引入完整的感光细胞模拟光和二磷酸甘油酸的作用，其抑制三磷酸肌醇和昏暗的光。因此，光激发的视紫红质与G蛋白的相互作用在脊椎动物和无脊椎动物的光感受器中是相似的。然而，这些G蛋白激活不同的感光酶：无脊椎动物中的磷脂酶C和脊椎动物中的cGMP磷酸二酯酶。
Fly photoreceptor membranes were used to test the effect on defined biochemical reactions of light and of compounds causing photoreceptor excitation. Complementary electrophysiological studies examined whether putative second messengers excite the fly photoreceptor cells. This analysis revealed the following sequence of events: photoexcited rhodopsin activates a G protein by facilitating GTP binding. The G protein then activates a phospholipase G that generates inositol trisphosphate, which in turn acts as an internal messenger to bring about depolarization of the photoreceptor cell. Binding assays of GTP analogs and measurements of GTPase activity showed that there are 1.6 million copies of G protein per photoreceptor cell. The GTP binding component is a 41-kDa protein, and the light-activated GTPase is dependent on photoconversion of rhodopsin to metarhodopsin. Analysis of phospholipase C activity revealed that this enzyme is under stringent control of the G protein, that the major product formed is inositol trisphosphate, and that this product is rapidly hydrolyzed by a specific phosphomonoesterase. Introduction of inositol trisphosphate to the intact photoreceptor cel mimics the effect of light, and bisphosphoglycerate, which inhibits inositol trisphosphate and of dim light. The interaction of photoexcited rhodopsin with a G protein is thus similar in both vertebrate and invertebrate photoreceptors. These G proteins, however, activate different photoreceptor enzymes: phospholipase C in invertebrates and cGMP phosphodiesterase in vertebrates.