Volume and enthalpy changes in the early steps of bacteriorhodopsin photocycle studied by time-resolved photoacoustics.
Volume and enthalpy changes in the early steps of bacteriorhodopsin photocycle studied by time-resolved photoacoustics.
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通过时间分辨光声学研究细菌视紫红质光循环早期步骤中的体积和焓变化。
DOI：
10.1016/s0006-3495(96)79235-4
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发表时间：
1996
影响因子：
3.4
通讯作者：
Mauzerall,D
中科院分区：
文献类型：
--
作者：
Zhang,D;Mauzerall,D
我们用脉冲、时间分辨光声研究了细菌视紫红质(BR)光循环早期阶段的光诱导体积变化、能量和动力学。我们的数据显示，有两个音量变化。快速的体积变化(<；或=200 ns)是一种膨胀(2.5+/-0.3A3/分子)，并且仅在紫膜(PM)中观察到，在3-[(3-胆酰胺丙基)-二甲基氨基]-1-丙烷-磺酸盐-磺酸盐溶解的BR样品中消失；缓慢的变化(约1微秒)是体积收缩(-3.7+/-0.3A3/分子)。快速膨胀归因于PM中聚集的BR的重组，以及1微米的收缩归因于Asp 212中水的氢键的变化(Kandori等人。1995年。J.Am化学。SoC。117：2118-2119)。K中间体的形成以热的形式释放了大部分吸收的能量，其增量为Hk=-36+/-8kJ/mol。K-->；L台阶的活化能为49+/-6kJ/mo1，热变较小，为-4+/-10kJ/mo1。在我们研究的时间尺度上，溶剂D2O取代H2O对初级光化学动力学、热焓和体积变化没有影响。比较单体和聚集BR的数据，我们得出结论：光循环的功能单元是BR单体，因为动力学(速率常数和活化能)和热变与其聚集状态无关。
We have studied the photoinduced volume changes, energetics, and kinetics in the early steps of the bacteriorhodopsin (BR) photocycle with pulsed, time-resolved photoacoustics. Our data show that there are two volume changes. The fast volume change ( < or=200 ns) is an expansion (2.5 +/- 0.3 A3/molecule) and is observed exclusively in the purple membrane (PM), vanishing in the 3-[(3-cholamidopropyl)-dimethylammonio] -1-propane-sulfonate-sulfonate-solubilized BR sample; the slow change (approximately 1 micros) is a volume contraction (-3.7 +/- 0.3 A3/molecule). The fast expansion is assigned to the restructuring of the aggregated BR in the PM, and the 1-micros contraction to the change in hydrogen bonding of water at Asp 212 (Kandori et al. 1995. J. Am. Chem. Soc. 117:2118–2119). The formation of the K intermediate releases most of the absorbed energy as heat, with delta Hk=-36 +/- 8 kJ/mol. The activation energy of the K --> L step is 49 +/- 6 kJ/mol, but the enthalpy change is small, -4 +/- 10 kJ/mol. On the time scale we studied, the primary photochemical kinetics, enthalpy, and volume changes are not affected by substituting the solvent D2O for H2O. Comparing data on monomeric and aggregated BR, we conclude that the functional unit for the photocycle is the BR monomer, because both the kinetics (rate constant and activation energy) and the enthalpy changes are independent of its aggregation state.