水合电子与亚铁细胞色素c反应的机制。

Mechanism of the reaction of hydrated electrons with ferrocytochrome c.

Butler J, De Kok J, De Weille J R, Koppenol W H, Braams R

Biochim Biophys Acta. 1977 Feb 7;459(2):207-15. doi: 10.1016/0005-2728(77)90022-6.

Abstract

The hydrated electron reacts with ferrocytochrome c to form an unstable intermediate. This intermediate decays in a first-order manner to give, in the first instance, a product which has a similar absorption spectrum in the range 400-610 nm as normal ferricytochrome c. 2. At 21 degrees C the rate constant for the reaction of hydrated electrons with ferrocytochrome c at pH 7.4 (2 mM phosphate buffer) is (3.0 +/- 0.3) = 10(10) M-1 - S-1. As the pH is increased above pH 8.0 the rate constant steadily decreases. The dependence of the rate constant on pH can be explained if ferrocytochrome c has a pK of around 9.2. 3. At 21 degrees C and pH 7.4, the rate constant for the decay of the intermediate is (1.40 +/- 0.15) - 10(5) S-1. This reaction shows no pH dependence in the range 6-2-11.0. 4. A mechanism is proposed whereby the central metal atom of the ferrocytochrome c is oxidased and a thioether bond is reduced. The resulting ferricytochrome c species then slowly develops an absorbance at 606 nm due to the attack of the sulfhydryl group on the haem.

摘要

水合电子与亚铁细胞色素c反应形成不稳定的中间体。该中间体以一级反应方式衰变，首先产生一种在400 - 610 nm范围内具有与正常高铁细胞色素c相似吸收光谱的产物。2. 在21℃时，水合电子与pH 7.4（2 mM磷酸盐缓冲液）下的亚铁细胞色素c反应的速率常数为(3.0±0.3)×10¹⁰ M⁻¹·s⁻¹。当pH升高到8.0以上时，速率常数稳步下降。如果亚铁细胞色素c的pK约为9.2，则可以解释速率常数对pH的依赖性。3. 在21℃和pH 7.4时，中间体衰变的速率常数为(1.40±0.15)×10⁵ s⁻¹。该反应在6.2 - 11.0范围内没有pH依赖性。4. 提出了一种机制，据此亚铁细胞色素c的中心金属原子被氧化，硫醚键被还原。由于巯基对血红素的攻击，生成的高铁细胞色素c物种随后在606 nm处缓慢产生吸光度。