Rhodopsin and Porphyropsin Fields In the Adult Bullfrog Retina
Rhodopsin and Porphyropsin Fields In the Adult Bullfrog Retina
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成年牛蛙视网膜中的视紫红质和紫质视场
DOI：
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发表时间：
1971
期刊：
影响因子：
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通讯作者：
G. Wald
中科院分区：
文献类型：
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作者：
T. Reuter;Richard H. White;G. Wald
虽然早先人们认为牛蛙的视觉系统经历了从蝌蚪的维生素A2和视紫红质到成年的维生素A1和视紫红质的几乎完全的变态，但目前的观察表明，成年蛙的视网膜可能含有多达30-40%的视紫红质，所有这些都分离在背侧区。成年人视网膜的最背侧的四分之一可能含有81-89%的紫质蛋白和少量的视紫红质;腹侧的一半只含有视紫红质。此外，背侧区包含比腹侧视网膜高两到三倍的视色素浓度。视网膜下面的色素上皮含有维生素A1和A2的相应分布，主要是维生素A2在背侧色素上皮中，仅维生素A1在腹侧区中。视网膜接受色素上皮细胞提供的任何维生素A，并将其转化为相应的视觉色素。因此，一片光适应的背侧视网膜放置在腹侧色素上皮再生视紫红质，而一片光适应的腹侧视网膜放置在背侧色素上皮再生主要是紫质蛋白。维生素A2必须由维生素A1通过在环中的3，4-键处脱氢而制成。这种转化必须发生在色素上皮中，推测是通过维生素A-3，4-脱氢酶的作用。变态时的基本变化是使这种脱氢酶减少，并将其隔离在背色素上皮中。一些成年牛蛙，也许是在夏天拍摄的，含有非常少的卟啉蛋白酶--可能只有5%--仍然隐藏在背侧视网膜中。视网膜表面上的光梯度对这种分布几乎没有影响。视网膜背侧的视色素密度更大，也许也是--尽管这一点还不太清楚--视紫蛋白在这一区域的存在，在增加视网膜对从下面接收到的较暗的光和有时较红的光的敏感性方面具有一定的生态重要性。
Though it had been supposed earlier that the bullfrog undergoes a virtually complete metamorphosis of visual systems from vitamin A2 and porphyropsin in the tadpole to vitamin A1 and rhodopsin in the adult, the present observations show that the retina of the adult frog may contain as much as 30–40% porphyropsin, all of it segregated in the dorsal zone. The most dorsal quarter of the adult retina may contain 81–89% porphyropsin mixed with a minor amount of rhodopsin; the ventral half contains only rhodopsin. Further, the dorsal zone contains a two to three times higher concentration of visual pigments than the ventral retina. The pigment epithelium underlying the retina contains a corresponding distribution of vitamins A1 and A2, predominantly vitamin A2 in the dorsal pigment epithelium, exclusively vitamin A1 in the ventral zone. The retina accepts whatever vitamin A the pigment epithelium provides it with, and turns it into the corresponding visual pigment. Thus, a piece of light-adapted dorsal retina laid back on ventral pigment epithelium regenerates rhodopsin, whereas a piece of light-adapted ventral retina laid back on dorsal pigment epithelium regenerates predominantly porphyropsin. Vitamin A2 must be made from vitamin A1, by dehydrogenation at the 3,4-bond in the ring. This conversion must occur in the pigment epithelium, presumably through the action of a vitamin A-3,4-dehydrogenase. The essential change at metamorphosis is to make much less of this dehydrogenase, and to sequester it in the dorsal pigment epithelium. Some adult bullfrogs, perhaps characteristically taken in the summer, contain very little porphyropsin—only perhaps 5%—still sequestered in the dorsal retina. The gradient of light over the retinal surface has little if any effect on this distribution. The greater density of visual pigments in the dorsal retina, and perhaps also—although this is less clear—the presence of porphyropsin in this zone, has some ecological importance in increasing the retinal sensitivity to the dimmer and, on occasion, redder light received from below.