Aspartic acids 96 and 85 play a central role in the function of bacteriorhodopsin as a proton pump.
Aspartic acids 96 and 85 play a central role in the function of bacteriorhodopsin as a proton pump.
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天冬氨酸 96 和 85 在细菌视紫红质作为质子泵的功能中发挥着核心作用。
作者：
Hans;K. Fendler;Ernst Bamberg;J. Tittor;Dieter Oesterhelt
报道了来自光合负盐细菌菌株的两个点突变细菌视紫红质（BR）的光谱和功能分析。来自菌株384的细菌视紫红质在位置85处含有谷氨酸而不是天冬氨酸，并且来自菌株326的BR在位置96处含有天冬酰胺而不是天冬氨酸。与野生型BR相比，BR Asp 85--Glu中的M形成加速约10倍，而BR Asp 96--Asn中的M衰减在pH 6下减慢约50倍。含有突变BR的紫色膜片定向并固定在聚丙烯酰胺凝胶中或吸附到平面脂质膜上。在各种条件下的光电流的测量动力学与观察到的光循环动力学一致。BR Asp 85--Glu的无效性在于在约610 nm处吸收最大的非活性物质占主导地位，而BR Asp 96--Asn由于其缓慢的光循环而无效。这些实验结果表明，天冬氨酸96在席夫碱的重质子化反应中起着至关重要的作用。这两个残基对于有效的质子泵都是必不可少的。
A spectroscopic and functional analysis of two point‐mutated bacteriorhodopsins (BRs) from phototrophic negative halobacterial strains is reported. Bacteriorhodopsin from strain 384 contains a glutamic acid instead of an aspartic acid at position 85 and BR from strain 326 contains asparagine instead of aspartic acid at position 96. Compared to wild‐type BR, the M formation in BR Asp85–‐Glu is accwelerated approximately 10‐fold, whereas the M decay in BR Asp96–‐Asn is slowed down approximately 50‐fold at pH6. Purple membrane sheets containing the mutated BRs were oriented and immobilized in polyacrylamide gels or adsorbed to planar lipid films. The measured kinetics of the photocurrents under various conditions agree with the observed photocycle kinetics. The ineffectivity of BR Asp85–‐Glu resides in the dominance of an inactive species absorbing maximally at approximately 610 nm, while BR Asp96–‐Asn is ineffective due to its slow photocycle. These experimental results suggest that aspartic acid 96 plays a crucial role for the reprotonation of the Schiff base. Both residues are essential for an effective proton pump.