Gennis Robert B
Department of Biochemistry, University of Illinois, 600 South Mathews Avenue, Urbana, IL 61801, USA.
Front Biosci. 2004 Jan 1;9:581-91. doi: 10.2741/1237.
Cytochrome oxidase catalyzes the four-electron reduction of O2 to water and conserves the substantial free energy of the reaction in the form of a protonmotive force. For each electron, two full charges are translocated across the membrane, resulting in a voltage. One of the mechanisms to generate the charge separation in cytochrome oxidase is via a proton pump. A single reaction cycle can be monitored over the course of about 1 msec using absorption spectroscopy, revealing distinct intermediates. Thus, the reaction cycle can be studied as a series of steps. Each of the reaction steps in the catalytic cycle involves a sequence of coupled electron and proton transfer reaction, where protons are either consumed in the chemistry of water formation or pumped across the membrane. The pumping mechanism requires consideration of both the thermodynamics of the various species but also the favored kinetic pathways that assure proton pumping is unidirectional. Hence, a knowledge of transition states and transiently, poorly populated intermediates is likely to be important to understand the mechanism of the pump.
细胞色素氧化酶催化将O2四电子还原为水，并以质子动力的形式保存反应中大量的自由能。对于每个电子，有两个完整的电荷跨膜转运，从而产生电压。细胞色素氧化酶中产生电荷分离的机制之一是通过质子泵。使用吸收光谱法可以在大约1毫秒的过程中监测单个反应循环，揭示不同的中间体。因此，反应循环可以作为一系列步骤来研究。催化循环中的每个反应步骤都涉及一系列耦合的电子和质子转移反应，其中质子要么在水形成的化学反应中被消耗，要么被泵过膜。泵送机制既需要考虑各种物质的热力学，也需要考虑确保质子泵送是单向的有利动力学途径。因此，了解过渡态以及瞬时存在的、数量稀少的中间体对于理解泵的机制可能很重要。
