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首页> 外文期刊>Biochemistry >Internal electron transfer in cytochrome c oxidase from Rhodobacter sphaeroides.
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Internal electron transfer in cytochrome c oxidase from Rhodobacter sphaeroides.

机译：来自乳菌氏菌的细胞色素C氧化酶内电子转移。

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摘要

Absorbance changes following CO dissociation by flash photolysis from mixed-valence aa3 cytochrome oxidase from Rhodobacter sphaeroides have been followed in the Soret and alpha regions. They reflect internal electron transfer in the partially reduced enzyme, and the kinetics of the reactions has been determined. As with the bovine enzyme, three kinetic phases are found with relaxation time constants at neutral pH of about 3 microseconds, 35 microseconds, and 1 ms. The first reaction phase represents electron transfer from cytochrome a3 to cytochrome a, and the extent of this reaction is about 3 times larger compared to the bovine enzyme. The energetics of the reaction has been analyzed on the basis of measurements of its temperature dependence. The reorganization energy is close to 120 kJ mol-1, and it is suggested that this rather high value is the result of changes in solvation at the cytochrome a3-CuB site. The subsequent electron transfer between cytochrome a and CuA, with a time constant of 35 microseconds, is almost activationless and has a very low reorganization energy. The final phase, with a time constant close to 1 ms at neutral pH, represents a further shift in the equilibrium between cytochrome a3 and cytochrome a, and it is limited by proton-transfer reactions. The pKa values of the groups involved are significantly shifted in the bacterial oxidase compared to the bovine one. The total extent of electron transfer in the three backflow reactions has also been determined by a comparison of the CO-recombination rates in the mixed-valence and fully reduced enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)
机译：在Soret和Alpha区遵循来自闪光术AA3细胞色素氧化酶的CO通过闪光分离的吸光度变化已经过于索孢子和α3。它们反映了部分减少的酶中的内部电子传递，并确定了反应的动力学。与牛酶一样，在中性pH下的弛豫时间常数为约3微秒，35微秒和1ms，发现三个动力学相。第一反应相代表示来自细胞色素A3至细胞色素A的电子转移，与牛酶相比，该反应的程度约为3倍。在测量其温度依赖性的基础上分析了反应的能量。重组能量接近120 kJ mol-1，并且建议这种相当高的值是细胞色素A3-CUB位点在溶剂化变化的结果。随后的细胞色A和CUA之间的电子传递，具有35微秒的时间常数，几乎活化并且具有非常低的重组能量。最终阶段，在中性pH下近1ms的时间常数，表示细胞色素A3和细胞色素A之间的平衡进一步变化，并且受质子转移反应的限制。与牛1相比，所涉及的组的PKA值在细菌氧化酶中显着移位。通过比较混合价和完全减少的酶的共复合速率的比较来确定三个回流反应中的电子转移的总程度。（抽象截断为250字）

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