Photoreactions of bacteriorhodopsin at acid pH.-猫眼课题宝

细菌视紫红质在酸性 pH 下的光反应。

DOI：

10.1016/s0006-3495(89)82761-4

发表时间：

1989

期刊：

Biophysical journal

影响因子：

3.4

通讯作者：

中科院分区：

生物学3区

文献类型：

作者：

Váró,G;Lanyi,JK

人们已经知道，细菌视紫红质，视网膜蛋白质的紫膜，其功能作为光驱动的质子泵，在酸性pH值进行可逆的光谱变化。各种细菌视紫红质物种的吸收光谱估计从测量光谱的混合物，在低pH值下形成，在硫酸盐和氯化物的存在下。这些对pH值和Cl-浓度的依赖性符合一个模型，其中紫色膜的逐步质子化产生“蓝膜”，其将结合，随着pH值的降低，氯离子的亲和力增加，产生“酸性紫色膜”。“使用多通道分析仪的瞬态光谱法鉴定了这些改变的颜料的光循环的中间体，并描述了它们的动力学。蓝膜产生红移KL样和L样的产品，但没有其他的光中间体，与早期的建议一致。然而，与其他人不同的是，我们发现酸性紫膜表现出非常不同的光循环：它的第一个检测到的中间体不像KL，因为它的红移要大得多，而唯一的其他中间体类似于细菌视紫红质光循环的O物质。在这两种光循环中都没有发现具有去质子化希夫碱的类M中间体。在细菌视紫红质的酸形式和氯离子转运系统盐视紫红质的光反应之间存在显著的相似性，其中席夫碱去质子化似乎是由于缺乏合适的天冬氨酸残基而不是由于低pH而被阻止的。

It has been known that bacteriorhodopsin, the retinal protein in purple membrane which functions as a light-driven proton pump, undergoes reversible spectroscopic changes at acid pH. The absorption spectra of various bacteriorhodopsin species were estimated from measured spectra of the mixtures that form at low pH, in the presence of sulfate and chloride. The dependency of these on pH and the concentration of Cl- fit a model in which progressive protonation of purple membrane produces "blue membrane", which will bind, with increasing affinity as the pH is lowered, chloride ions to produce "acid purple membrane." Transient spectroscopy with a multichannel analyzer identified the intermediates of the photocycles of these altered pigments, and described their kinetics. Blue membrane produced red-shifted KL-like and L-like products, but no other photointermediates, consistent with earlier suggestions. Unlike others, however, we found that acid purple membrane exhibited a very different photocycle: its first detected intermediate was not like KL in that it was much more red-shifted, and the only other intermediate detectable resembled the O species of the bacteriorhodopsin photocycle. An M-like intermediate, with a deprotonated Schiff base, was not found in either of these photocycles. There are remarkable similarities between the photoreactions of the acid forms of bacteriorhodopsin and the chloride transport system halorhodopsin, where the Schiff base deprotonation seems to be prevented by lack of suitable aspartate residues, rather than by low pH.