Existence of two substates in the O intermediate of the bacteriorhodopsin photocycle
Existence of two substates in the O intermediate of the bacteriorhodopsin photocycle
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细菌视紫红质光循环的 O 中间体中存在两种亚态
DOI：
10.1016/j.bbamem.2022.183998
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Ihara Kunio
中科院分区：
文献类型：
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作者：
Kouyama Tsutomu;Ihara Kunio
13-转构象的视网膜发色团光异构为13-顺构象时，细菌视紫红质（bR）的质子泵送循环启动。为了了解在光循环后期发生的初始视网膜结构的恢复过程，我们对在不同pH水平和不同盐浓度下收集的吸收动力学数据进行了全面分析。分析结果揭示了转热循环后期的以下特征。i) O中间体中有两个基态。ii)第一亚态（O1）的可见吸收波段出现在比后亚态（O2）短得多的波长上。iii) O1与前态(N)处于快速平衡状态，但当pKa值为6.5 （2 M KCl）的可电离残留物（X1）去质子化时，O1的稳定性低于N。iv)在低pH和低盐浓度下，O2的衰变时间常数比前两种状态的衰变时间常数长，但随着介质pH和盐浓度的增加，时间常数之间的关系发生变化。根据目前的观察和以往对O中的发色团结构的研究，我们推测O中的视网膜发色团呈现扭曲的13顺式构型，并且O -to- o2的转变伴随着c13双键c14键的顺式到转异构化。
The proton pumping cycle of bacteriorhodopsin (bR) is initiated when the retinal chromophore with the 13-transconfiguration is photo-isomerized into the 13-cisconfiguration. To understand the recovery processes of the initial retinal configuration that occur in the late stage of the photocycle, we have performed a comprehensive analysis of absorption kinetics data collected at various pH levels and at different salt concentrations. The result of analysis revealed the following features of the late stages of thetransphotocycle.i) Two substates occur in the O intermediate.ii) The visible absorption band of the first substate (O1) appears at a much shorter wavelength than that of the late substate (O2).iii) O1 is in rapid equilibrium with the preceding state (N), but O1 becomes less stable than N when an ionizable residue (X1) with a pKa value of 6.5 (in 2 M KCl) is deprotonated.iv) At a low pH and at a low salt concentration, the decay time constant of O2 is longer than those of the preceding states, but the relationship between these time constants is altered when the medium pH or the salt concentration is increased. On the basis of the present observations and previous studies on the structure of the chromophore in O, we suspect that the retinal chromophore in O1 takes on a distorted 13-cisconfiguration and the O1-to-O2 transition is accompanied bycis-to-transisomerization about C13double bondC14 bond.