Shichida Y, Okada T, Kandori H, Fukada Y, Yoshizawa T
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Biochemistry. 1993 Oct 12;32(40):10832-8. doi: 10.1021/bi00091a039.
The photobleaching process of iodopsin (a chicken red-sensitive cone visual pigment) purified in a detergent system containing CHAPS and phosphatidylcholine was investigated by means of nanosecond laser photolysis at room temperature. Excitation of iodopsin with a nanosecond laser pulse (wavelength, 560 nm; pulse width, 17 ns) resulted in the formation of at least four intermediates on the nanosecond to millisecond time scale. The earliest intermediate detected had an absorption maximum at 571 nm, which was very close to that of original iodopsin (lambda max = 567 nm), and remarkably blue-shifted as compared with that of bathoiodopsin [lambda max = 625 nm; Kandori et al. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 8908-8912]. The intermediate, named BL-iodopsin, converted to the next intermediate, lumiiodopsin (lambda max = 535 nm), with a time constant of 130 ns. The BL intermediate had an absorption maximum just between batho- and lumiiodopsins, and an extinction coefficient comparable with these intermediates. These properties are different from those of the corresponding intermediate of rhodopsin [BL(BSI)-rhodopsin], suggesting that the binding of chloride to iodopsin, but not to rhodopsin, has an influence upon changes of the chromophore-opsin interaction in the early stage of photobleaching of iodopsin. Lumiiodopsin converted to metaiodopsin I (lambda max < 500 nm) with a time constant of 230 microseconds, and then to metaiodopsin II (lambda max = 390 nm) with a time constant of 6 ms. A thermal equilibrium between metaiodopsin I and II was established, but unlike meta intermediates of rhodopsin, they showed little temperature dependence.
在含有CHAPS和磷脂酰胆碱的去污剂体系中纯化的视碘质（一种鸡的红色敏感视锥视觉色素）的光漂白过程，于室温下通过纳秒激光光解进行了研究。用纳秒激光脉冲（波长560 nm；脉冲宽度17 ns）激发视碘质，在纳秒至毫秒时间尺度上产生了至少四种中间体。检测到的最早中间体在571 nm处有最大吸收峰，这与原始视碘质的最大吸收峰（λmax = 567 nm）非常接近，并且与视紫红质（λmax = 625 nm；Kandori等人，(1990) Proc. Natl. Acad. Sci. U.S.A. 87, 8908 - 8912）相比有明显的蓝移。这个中间体被命名为BL - 视碘质，以130 ns的时间常数转化为下一个中间体，即发光视碘质（λmax = 535 nm）。BL中间体的最大吸收峰恰好在视紫红质和发光视碘质之间，并且消光系数与这些中间体相当。这些性质与视紫红质相应中间体（BL(BSI) - 视紫红质）的性质不同，这表明氯离子与视碘质而非视紫红质的结合，对视碘质光漂白早期发色团 - 视蛋白相互作用的变化有影响。发光视碘质以230微秒的时间常数转化为视碘质I（λmax < 500 nm），然后以6毫秒的时间常数转化为视碘质II（λmax = 390 nm）。视碘质I和II之间建立了热平衡，但与视紫红质的中间产物不同，它们几乎没有温度依赖性。
