Brandt U
Universitätsklinikum Frankfurt, Zentrum der Biologischen Chemie, Germany.
Biochim Biophys Acta. 1996 Jul 18;1275(1-2):41-6. doi: 10.1016/0005-2728(96)00048-5.
The overall electron- and proton-pathways within the cytochrome-bc1 complex are described by a widely accepted mechanism known as the protonmotive Q-cycle. Within this reaction scheme, the unique bifurcation of electron flow into a high potential and a low potential pathway occurring at the ubihydroquinone-oxidation center is the energy conserving reaction. It is this reaction, which results in vectorial proton translocation, as it allows the 'recycling' of every second electron across the membrane onto the ubiquinone-reduction center. However, the Q-cycle reaction scheme does not address the detailed chemistry of this central step. Based on a structural model of the ubihydroquinone-oxidation pocket and the assumption that the reaction involves two ubiquinone molecules in a stacked configuration, here I propose a detailed chemical model for the reactions occurring during steady-state catalysis. In this proton-gated charge-transfer mechanism the reaction is controlled by the deprotonation of the substrate ubihydroquinone and not, as proposed earlier, by the formation of a highly unstable semiquinone species.
细胞色素bc1复合物内的整体电子和质子途径由一种被广泛接受的机制——质子动力Q循环来描述。在这个反应体系中，在泛醇氧化中心发生的电子流独特地分支为高电位和低电位途径，这是能量守恒反应。正是这个反应导致了质子的矢量跨膜转运，因为它允许每第二个电子“循环”穿过膜回到泛醌还原中心。然而，Q循环反应体系并未涉及这一核心步骤的详细化学过程。基于泛醇氧化口袋的结构模型以及反应涉及两个呈堆叠构型的泛醌分子这一假设，在此我提出一个关于稳态催化过程中发生反应的详细化学模型。在这个质子门控电荷转移机制中，反应由底物泛醇的去质子化控制，而不是像之前所提出的那样，由形成高度不稳定的半醌物种来控制。
