Seki T
J Gen Physiol. 1984 Jul;84(1):49-62. doi: 10.1085/jgp.84.1.49.
Aporetinochrome, which is a protein moiety of retinochrome without chromophore retinal, is found in the membrane containing retinochrome. All of the prosthetic retinal of retinochrome in membranes, which is all-trans retinal, is bound to the chromophoric site on the protein moiety, with protonated Schiff bases showing an absorption band with the maximum at 495 nm. On exposure to light, retinochrome is converted to metaretinochrome at room temperature. The prosthetic retinals of metaretinochrome in membranes, which are 11-cis retinals, are in two states: retinals bound to the chromophoric site with protonated Schiff bases, and the free retinals, which are separated from the protein moiety. These states are suggested from the following observations. (a) The ratio of the absorbance at 470 nm of metaretinochrome to that at 495 nm of the parental retinochrome differs because of differences in samples and is higher in the purer preparations. (b) The difference spectrum of absorption of metaretinochrome caused by alkalinization shows two minimum peaks at approximately 420 and 470 nm. (c) The rate of bleaching of metaretinochrome in membranes with dilute NH2OH is much faster than that of retinochrome, and the absorption band in the near-UV region is more susceptible to NH2OH than the visible absorption band. The state of the prosthetic retinals in metaretinochrome was confirmed directly by the reaction of metaretinochrome in membranes with NaBH4. After treatment with NaBH4, the sodium dodecyl sulfate-polyacrylamide gel electrophoretic pattern shows two fluorescent bands: one at the position that corresponds to the retinochrome protein (mol wt 27,000 +/- 2,000), and another at the front of migration, where no band of protein is observed. Retinoids extracted from the NaBH4-treated metaretinochrome in membranes and analyzed with high-pressure liquid chromatography show a main peak of 11-cis retinol. The results of this and earlier (Seki et al., 1982) papers are summarized, and it is strongly suggested that metaretinochrome in the squid retina may play the role of 11-cis retinal donor for opsin and contribute to the synthesis of the squid rhodopsin.
脱辅视色素是视色素的蛋白质部分，不含发色团视黄醛，存在于含有视色素的膜中。膜中视色素的所有辅基视黄醛均为全反式视黄醛，它与蛋白质部分的发色团位点结合，质子化席夫碱在495nm处有一个吸收带最大值。在光照下，视色素在室温下会转化为变视色素。膜中变视色素的辅基视黄醛为11-顺式视黄醛，处于两种状态：与质子化席夫碱结合在发色团位点的视黄醛，以及与蛋白质部分分离的游离视黄醛。这些状态可从以下观察结果推断得出。（a）由于样品不同，变视色素在470nm处的吸光度与亲本视色素在495nm处的吸光度之比存在差异，且在纯度更高的制剂中该比值更高。（b）碱化导致的变视色素吸收差异光谱在约420和470nm处有两个最小峰。（c）膜中变视色素用稀NH2OH漂白的速率比视色素快得多，近紫外区域的吸收带比可见吸收带更容易受到NH2OH的影响。变视色素中辅基视黄醛的状态通过膜中变视色素与NaBH4的反应直接得到证实。用NaBH4处理后，十二烷基硫酸钠-聚丙烯酰胺凝胶电泳图谱显示出两条荧光带：一条位于与视色素蛋白相对应的位置（分子量27,000±2,000），另一条在迁移前沿，此处未观察到蛋白条带。从膜中经NaBH4处理的变视色素中提取并通过高压液相色谱分析的类视黄醇显示出一个11-顺式视黄醇的主峰。总结了本文及早期（Seki等人，1982年）论文的结果，强烈表明鱿鱼视网膜中的变视色素可能作为视蛋白的11-顺式视黄醛供体发挥作用，并有助于鱿鱼视紫红质的合成。
