Brunori M, Giuffré A, Malatesta F, Sarti P
Department of Biochemical Sciences A Rossi-Fanelli and CNR Center for Molecular Biology, University of Rome La Sapienza, Italy.
J Bioenerg Biomembr. 1998 Feb;30(1):41-5. doi: 10.1023/a:1020503410377.
Novel experimental evidence is presented further supporting the hypothesis that, starting with resting oxidized cytochrome c oxidase, the internal electron transfer to the oxygen binding site is kinetically controlled. The reduction of the enzyme was followed spectroscopically and in the presence of NO or CO, used as trapping ligands for reduced cytochrome a3; ruthenium hexamine was used as a spectroscopically silent electron donor. Consistent with the high combination rate constant for reduced cytochrome a3, NO proved to be a very efficient trapping ligand, while CO did not. The results are discussed in view of two alternative (thermodynamic and kinetic) hypotheses of control of electron transfer to the binuclear (cyt.a3-CuB) center. Fulfilling the prediction of the kinetic control hypothesis: i) the reduction of cytochrome a3 and ligation are synchronous and proceed at the intrinsic rate of cytochrome a3 reduction, ii) the measured rate of formation of the nitrosyl derivative is independent of the concentration of both the reductant and NO.
本文提供了新的实验证据，进一步支持了以下假说：从静息态氧化型细胞色素c氧化酶开始，向氧结合位点的内部电子转移受动力学控制。通过光谱法跟踪酶的还原过程，并在存在一氧化氮（NO）或一氧化碳（CO）的情况下进行，NO和CO用作还原型细胞色素a3的捕获配体；六胺钌用作光谱学上无信号的电子供体。与还原型细胞色素a3的高结合速率常数一致，NO被证明是一种非常有效的捕获配体，而CO则不是。结合电子转移至双核（细胞色素a3-CuB）中心的两种替代假说（热力学和动力学）对结果进行了讨论。满足动力学控制假说的预测：i）细胞色素a3的还原和配位是同步的，并以细胞色素a3还原的固有速率进行，ii）测得的亚硝酰基衍生物的形成速率与还原剂和NO的浓度均无关。
