Murphy M P, Brand M D
Department of Biochemistry, University of Cambridge, England.
Eur J Biochem. 1988 May 2;173(3):645-51. doi: 10.1111/j.1432-1033.1988.tb14047.x.
The q+/2e stoichiometries (number of charges translocated per electron pair transferred) of cytochrome oxidase and the cytochrome bc1 complex in rat liver mitochondria were determined at a range of membrane potentials up to 180 mV. The method used was similar to the one used in the preceding paper by us in this journal to determine the q+/O stoichiometry of the mitochondrial electron transport chain from succinate to oxygen. The measured q+/2e stoichiometry of cytochrome oxidase was 3.5 positive charges per O atom reduced at low membrane potential (120 mV) and it decreased to about 1.5 at high membrane potential (180 mV). The measured q+/2e stoichiometry of the cytochrome bc1 complex was between 1 and 1.25 positive charges ejected per electron pair and did not change significantly as delta psi was varied from 85 mV to 157 mV. The sum of the q+/2e stoichiometries of cytochrome oxidase and the cytochrome bc1 complex determined separately was similar to their value determined together for electron transport from succinate to oxygen over the range of membrane potentials studied. The most probable interpretation of these results is that the stoichiometry of the cytochrome bc1 complex is invariant over a range of membrane potentials and that the q+/2e stoichiometry of cytochrome oxidase decreases from 4 at low membrane potential to 2 at high membrane potential.
在高达180 mV的一系列膜电位下，测定了大鼠肝线粒体中细胞色素氧化酶和细胞色素bc1复合物的q+/2e化学计量比（每转移一对电子所转运的电荷量）。所采用的方法与我们在本期刊上发表的前一篇论文中用于测定从琥珀酸到氧气的线粒体电子传递链的q+/O化学计量比的方法相似。测得的细胞色素氧化酶的q+/2e化学计量比在低膜电位（120 mV）下为每还原一个O原子3.5个正电荷，在高膜电位（180 mV）下降至约1.5个正电荷。测得的细胞色素bc1复合物的q+/2e化学计量比为每对电子排出1至1.25个正电荷，并且当膜电位差从85 mV变化到157 mV时没有显著变化。在研究的膜电位范围内，分别测定的细胞色素氧化酶和细胞色素bc1复合物的q+/2e化学计量比之和与它们一起测定的从琥珀酸到氧气的电子传递的值相似。这些结果最可能的解释是，细胞色素bc1复合物的化学计量比在一定范围的膜电位内是不变的，并且细胞色素氧化酶的q+/2e化学计量比从低膜电位下的4降至高膜电位下的2。
