Primary photochemical event in vision: proton translocation.
Primary photochemical event in vision: proton translocation.
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视觉中的主要光化学事件：质子易位。
DOI：
10.1073/pnas.74.8.3119
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发表时间：
1977
影响因子：
11.1
通讯作者：
P. Rentzepis
中科院分区：
文献类型：
--
作者：
K. Peters;M. Applebury;P. Rentzepis
为了直接观察前光视紫红质（视觉通路中的第一个中间体）的上升时间，对低温玻璃中的视紫红质进行了皮秒研究。只有在 20 K 或更低的温度下才能解析该中间体的上升时间，即使在 4 K 下，它的上升时间也快得惊人，约为 36 皮秒。对前光视紫红质形成速率的阿伦尼乌斯对温度的依赖性的检查表明，在低温下，线性有很大的偏差，即非阿伦尼乌斯行为。这种明显的非线性行为是量子力学隧道事件（例如氢的易位）的特征。隧道过程的一个很好的候选者是视蛋白与其视网膜发色团之间形成的质子化希夫碱的氢。氘交换视紫红质，其中希夫碱氢被氘取代，在低温下也表现出明显的非阿累尼乌斯温度依赖性，这与隧道效应一致。氘交换样品中前光视紫红质的形成速率要慢得多，并且观察到大约或等于 7 的氘同位素效应 kH/kD。该数据支持一个模型，其中前光视紫红质的形成涉及质子向视网膜发色团的席夫碱氮的易位。
Picosecond studies of rhodopsin in low-temperature glasses have been carried out in order to observe directly the risetime of prelumirhodopsin, the first intermediate in the visual pathway. Only at 20 K or below can the risetime of this intermediate be resolved and even at 4 K it is astoundingly rapid, about 36 psec. An examination of the Arrhenius dependence on temperature of the rate of formation of prelumirhodopsin shows a strong deviation from linearity at low temperatures, i.e., non-Arrhenius behavior. This marked non-linear behavior is characteristic of a quantum mechanical tunneling event such as the translocation of hydrogen. An excellent candidate for the tunnelling process is the hydrogen of the protonated Schiff base formed between opsin and its retinal chromophore. Deuterium-exchanged rhodopsin, in which the Schiff base hydrogen is replaced by a deuterium, also shows a marked non-Arrhenius temperature dependence at low temperatures, consistent with tunneling. The rate of formation of prelumirhodopsin in deuterium-exchanged samples is much slower and a deuterium isotope effect kH/kD approximately or equal to 7 is observed. The data support a model in which the formation of prelumirhodopsin involves translocation of a proton toward the Schiff base nitrogen of the retinal chromophore.