Tóth-Boconádi R, Dér A, Keszthelyi L
Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences, Szeged H-6701, Hungary.
Biophys J. 2000 Jun;78(6):3170-7. doi: 10.1016/S0006-3495(00)76853-6.
Buffers change the electric signals of light-excited bacteriorhodopsin molecules in purple membrane if their concentration and the pH of the low-salt solution are properly selected. "Positive" buffers produce a positive component, and "negative" buffers a negative component in addition to the signals due to proton pumping. Measurement of the buffer effects in the presence of glycyl-glycine or bis-tris propane revealed an increase of approximately 2 and a change of sign and a decrease to approximately -0.5 in the translocated charge in these cases, respectively. These factors do not depend on temperature. The Arrhenius parameters established from the evaluation of the kinetics indicate activation enthalpies of 35-40 kJ/mol and negative activation entropies for the additional signals. These values agree with those found by surface-bound pH-sensitive probes in the search of the timing of proton release and uptake. The electric signals were also measured in the case of D(2)O solutions with similar results, except for the increased lifetimes. We offer a unified explanation for the data obtained with surface-bound probes and electric signals based on the clusters at extracellular and cytoplasmic sites of bacteriorhodopsin participating in proton release and uptake.
如果适当选择缓冲液的浓度和低盐溶液的pH值，缓冲液会改变紫膜中光激发细菌视紫红质分子的电信号。“正”缓冲液除了产生质子泵引起的信号外，还会产生一个正分量，而“负”缓冲液会产生一个负分量。在甘氨酰甘氨酸或双三羟甲基氨基甲烷存在下测量缓冲液效应，结果显示在这些情况下，转移电荷量分别增加约2、符号改变并降至约-0.5。这些因素与温度无关。通过动力学评估确定的阿伦尼乌斯参数表明，额外信号的活化焓为35 - 40 kJ/mol，活化熵为负。这些值与表面结合的pH敏感探针在寻找质子释放和摄取时间时所发现的值一致。在重水溶液的情况下也测量了电信号，除了寿命增加外，结果相似。我们基于细菌视紫红质细胞外和细胞质位点参与质子释放和摄取的簇，对通过表面结合探针和电信号获得的数据提供了统一的解释。
