IODOPSIN
IODOPSIN
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DOI：
10.1085/jgp.38.5.623
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发表时间：
1955-01-01
影响因子：
3.8
通讯作者：
SMITH, PH
中科院分区：
文献类型：
--
作者：
WALD, G;BROWN, PK;SMITH, PH
在鸡视网膜的视锥细胞中发现的碘视蛋白系统与其类胡萝卜素中的视紫红质系统相同。它的区别仅在于与类胡萝卜素结合的蛋白质-视蛋白。视锥蛋白可称为视黄蛋白，以区别于视杆细胞的视黄蛋白。碘视黄蛋白在光照下漂白成视黄蛋白和全反式视黄烯的混合物。后者被乙醇脱氢酶和辅酶酶还原为全反式维生素A1。碘视蛋白是由维生素A和维生素A的酸异构体再合成的，新维生素A或相应的新视黄酸，与形成视紫红质的异构体相同。以新视黄酸和新视黄烯为原料合成碘视黄酸是一个自发反应。第二种顺视黄烯，异视黄烯a，形成异碘视蛋白（λ max 510 mµ）。碘视蛋白在中等光照下的漂白是一级反应（布利斯）。由新视黄带视蛋白合成碘视蛋白是二级反应，类似于视紫红质，但要快得多。在10°C。碘视蛋白合成的速度常数是视紫红质合成速度常数的527倍。视紫红质在pH 4-9的溶液中相当稳定，而碘视蛋白仅在pH 5-7下稳定，并且在更多的酸或碱性反应中迅速衰变。巯基毒物，对氯汞苯甲酸盐，阻止碘视蛋白的合成，就像阻止视紫红质一样。在不攻击视紫红质的浓度下，它也能漂白碘视蛋白。羟胺也能漂白碘视蛋白，但不会毒害它的合成。羟胺通过与视蛋白竞争视色素起作用。它能成功地与鸡、牛或青蛙的暗视蛋白竞争，从而阻断视紫红质的合成;但它捕获视黄质的效率低于黑视黄质，因此不能阻断碘视黄质的合成。虽然碘视黄质还没有制备成纯的形式，但它的吸收光谱已经通过两个独立的程序计算出来。这显示出λ max为562 mµ的α带，最小值约为435 mµ，以及近紫外线中约为370 mµ的小λ带。视锥细胞中碘视蛋白的低浓度解释了其高阈值的第一近似值，与视紫红质相比，碘视蛋白的合成相对较快，与视锥细胞的暗适应相对较快相对应，棒。本文导出了视敏度的对数与视杆细胞和视锥细胞中视色素浓度之间的理论关系。视杆细胞和视锥细胞的暗适应过程与视紫红质和碘视蛋白在溶液中的合成过程非常相似，视杆细胞和视锥细胞的光谱敏感性以及浦肯野现象都来源于视紫红质和碘视蛋白的吸收光谱。在鸡中，只有粗略的光谱灵敏度测量，这种关系只能近似地证明。鸽子的暗视敏感度与视紫红质的光谱相匹配，但明视敏感度主要或全部通过鸽子视锥中有色油球的过滤作用而向红色移动。在猫、豚鼠、蛇和青蛙中，没有这种有色的眼睛结构的干预，暗视和明视的灵敏度定量地匹配视紫红质和碘视蛋白的吸收光谱。在人类中，暗视敏感度与视紫红质的吸收光谱相匹配;但明视敏感度，当不被透镜和黄斑的黄色色素所扭曲时，位于比碘视蛋白更短的波长处。这种差异是预期的，因为人类的明视敏感度代表了至少三类与颜色有关的锥细胞的复合物。
The iodopsin system found in the cones of the chicken retina is identical with the rhodopsin system in its carotenoids. It differs only in the protein—the opsin —with which carotenoid combines. The cone protein may be called photopsin to distinguish it from thescotopsinsof the rods.Iodopsin bleaches in the light to a mixture of photopsin and all-trans retinene. The latter is reduced by alcohol dehydrogenase and cozymase to all-trans vitamin A1. Iodopsin is resynthesized from photopsin and acisisomer of vitamin A, neovitamin Abor the corresponding neoretineneb, the same isomer that forms rhodopsin. The synthesis of iodopsin from photopsin and neoretinenebis a spontaneous reaction. A secondcisretinene, isoretinene a, forms iso-iodopsin (λmax510 mµ).The bleaching of iodopsin in moderate light is a first-order reaction (Bliss). The synthesis of iodopsin from neoretineneband opsin is second-order, like that of rhodopsin, but is very much more rapid. At 10°C. the velocity constant for iodopsin synthesis is 527 times that for rhodopsin synthesis.Whereas rhodopsin is reasonably stable in solution from pH 4–9, iodopsin is stable only at pH 5–7, and decays rapidly at more acid or alkaline reactions.The sulfhydryl poison,p-chloromercuribenzoate, blocks the synthesis of iodopsin, as of rhodopsin. It also bleaches iodopsin in concentrations which do not attack rhodopsin.Hydroxylamine also bleaches iodopsin, yet does not poison its synthesis. Hydroxylamine acts by competing with the opsins for retinene. It competes successfully with chicken, cattle, or frog scotopsin, and hence blocks rhodopsin synthesis; but it is less efficient than photopsin in trapping retinene, and hence does not block iodopsin synthesis.Though iodopsin has not yet been prepared in pure form, its absorption spectrum has been computed by two independent procedures. This exhibits an α-band with λmax562 mµ, a minimum at about 435 mµ, and a small ß-band in the near ultraviolet at about 370 mµ.The low concentration of iodopsin in the cones explains to a first approximation their high threshold, and hence their status as organs of daylight vision.The relatively rapid synthesis of iodopsin compared with rhodopsin parallels the relatively rapid dark adaptation of cones compared with rods. A theoretical relation is derived which links the logarithm of the visual sensitivity with the concentration of visual pigment in the rods and cones. Plotted in these terms, the course of rod and cone dark adaptation resembles closely the synthesis of rhodopsin and iodopsin in solution.The spectral sensitivities of rod and cone vision, and hence the Purkinje phenomenon, have their source in the absorption spectra of rhodopsin and iodopsin. In the chicken, for which only rough spectral sensitivity measurements are available, this relation can be demonstrated only approximately. In the pigeon the scotopic sensitivity matches the spectrum of rhodopsin; but the photopic sensitivity is displaced toward the red, largely or wholly through the filtering action of the colored oil globules in the pigeon cones. In cats, guinea pigs, snakes, and frogs, in which no such colored ocular structures intervene, the scotopic and photopic sensitivities match quantitatively the absorption spectra of rhodopsin and iodopsin. In man the scotopic sensitivity matches the absorption spectrum of rhodopsin; but the photopic sensitivity, when not distorted by the yellow pigmentations of the lens and macula lutea, lies at shorter wave lengths than iodopsin. This discrepancy is expected, for the human photopic sensitivity represents a composite of at least three classes of cone concerned with color …