Kinetics and pH dependence of light-induced deprotonation of the Schiff base of rhodopsin: possible coupling to proton uptake and formation of the active form of Meta II.
Kinetics and pH dependence of light-induced deprotonation of the Schiff base of rhodopsin: possible coupling to proton uptake and formation of the active form of Meta II.
复制标题
光诱导视紫红质希夫碱去质子化的动力学和 pH 依赖性：可能与质子摄取和 Meta II 活性形式的形成偶联。
DOI：
10.1023/a:1013139520437
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
Ebrey,TG
中科院分区：
文献类型：
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作者：
Kuwata,O;Yuan,C;Misra,S;Govindjee,R;Ebrey,TG
本文首先综述了有关Meta II形成的动力学、质子在Meta II形成中的作用和化学计量学、光诱导质子浓度变化的动力学以及质子吸收的位置。然后，我们继续比较导致细菌视紫红质中希夫碱去质子化的过程和视紫红质。我们指出，这两种定向色素分子的光诱导电信号符号的相似性可以解释为细菌视紫红质从其胞外一侧释放一个质子，而视紫红质从其胞质一侧吸收一个质子。然后，我们研究了牛视紫质中未光解状态的吸收光谱和Meta II形成的幅度和动力学对pH的依赖性。我们还测量了重氢和叠氮化物对Meta II形成的影响。我们得出结论：在未光解状态下，牛视紫质席夫碱的反离子和光解时占据一个质子的表面残基的pKa值都小于4。关于Meta II形成的pH依赖性的数据表明，所涉及的机制比漂白序列中两种顺序的、等谱的Meta II形式复杂得多。最后，我们检查了证据，就像细菌视紫红质一样，希夫碱的反离子(Glu113)的质子化与可质子化表面基团的pKa值的变化相耦合，称为视紫红质Z，并暂定为Glu134。我们的结论是，可能存在这样的耦合，导致了Meta II活性形式的形成。
In this paper we first review what is known about the kinetics of Meta II formation, the role and stoichiometry of protons in Meta II formation, the kinetics of the light-induced changes of proton concentration, and the site of proton uptake. We then go on to compare the processes that lead to the deprotonation of the Schiff base in bacteriorhodopsin with rhodopsin. We point out that the similarity of the signs of the light-induced electrical signals from the two kinds of oriented pigment molecules could be explained by bacteriorhodopsin releasing a proton from its extracellular side while rhodopsin taking up a proton on its cytoplasmic side. We then examined the pH dependence of both the absorption spectrum of the unphotolyzed state and the amplitude and kinetics of Meta II formation in bovine rhodopsin. We also measured the effect of deuteration and azide on Meta II formation. We concluded that the pKaof the counter-ion to the Schiff base of bovine rhodopsin and of a surface residue that takes up a proton upon photolysis are both less than 4 in the unphotolyzed state. The data on pH dependence of Meta II formation indicated that the mechanisms involved are more complicated than just two sequential, isospectral forms of Meta II in the bleaching sequence. Finally we examined the evidence that, like in bacteriorhodopsin, the protonation of the Schiff bases's counter-ion (Glu113) is coupled to the changing of the pKaof a protonatable surface group, called Z for rhodopsin and tentatively assigned to Glu134. We conclude that there probably is such a coupling, leading to the formation of the active form of Meta II.