Electron transfer rates and equilibrium within cytochrome c oxidase.
Electron transfer rates and equilibrium within cytochrome c oxidase.
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细胞色素 c 氧化酶内的电子转移速率和平衡。
DOI：
10.1046/j.1432-1327.2000.01072.x
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
Pecht,I
中科院分区：
文献类型：
--
作者：
Farver,O;Einarsdóttir,O;Pecht,I
用脉冲辐解法研究了牛细胞色素氧化酶中Cu A中心与血红素之间的分子内电子转移。在扩散控制反应中，CuA（初始电子受体）被1-甲基烟酰胺自由基还原，通过830 nm处的吸收变化监测。 在初始还原阶段之后，830 nm吸收部分恢复，对应于CuAcenter的再氧化。 同时，在445 nm和605 nm处的吸收增加，表明血红素减少。 血红素还原和CuRe氧化的速率常数在实验误差范围内是相同的，并且与酶浓度无关。这表明，一个快速的分子内电子平衡之间发生的CuA和血红素。在25 °C和pH 7.4下，CuA→ hemea ET和反向（hemea→ CuA）过程的速率常数分别为13 000 s− 1和3700 s−1。 这相当于在这些条件下的平衡常数为3.4。测定了ET反应的热力学参数和活化参数。这些结果的意义，特别是所观察到的低活化势垒，在已知的三维结构，ET途径和重组能量的框架内进行了讨论。
Intramolecular electron transfer (ET) between the CuAcenter and hemeain bovine cytochromecoxidase was investigated by pulse radiolysis. CuA, the initial electron acceptor, was reduced by 1‐methyl nicotinamide radicals in a diffusion‐controlled reaction, as monitored by absorption changes at 830 nm. After the initial reduction phase, the 830 nm absorption was partially restored, corresponding to reoxidation of the CuAcenter. Concomitantly, the absorption at 445 nm and 605 nm increased, indicating reduction of hemea. The rate constants for hemeareduction and CuAreoxidation were identical within experimental error and independent of the enzyme concentration. This demonstrates that a fast intramolecular electron equilibration is taking place between CuAand hemea. The rate constants for CuA→ hemeaET and the reverse (hemea→ CuA) process were found to be 13 000 s−1and 3700 s−1, respectively, at 25 °C and pH 7.4. This corresponds to an equilibrium constant of 3.4 under these conditions. Thermodynamic and activation parameters of the ET reactions were determined. The significance of these results, particularly the observed low activation barriers, are discussed within the framework of the known three‐dimensional structure, ET pathways and reorganization energies.