Fabian M, Palmer G
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251-1892.
Biochemistry. 1995 Feb 7;34(5):1534-40. doi: 10.1021/bi00005a009.
The interaction of peroxidatic derivatives of cytochrome c oxidase with cyanide has been investigated by optical spectroscopy and the stopped-flow method. Two reactions were found in the conversion of peroxy cytochrome oxidase to its cyanide complex. The first reaction is characterized by the loss of the 607 nm band, an increase in absorbance at 655 nm, and a decrease in absorbance at 432 nm resulting from a blue-shift of the Soret band; this reaction occurred with a bimolecular rate constant of about 90 M-1 s-1. The second reaction is observed as an absorbance increase at 585 and 432 nm; the latter was due to a red-shift of the Soret band. This second process proceeded with a rate constant of about 22 M-1 s-1. Both reaction rates are linearly dependent on the concentration of cyanide between 5 and 100 mM. The reappearance of the 655 nm band at the completion of the first reaction suggests that cytochrome a3 becomes transiently high-spin, a finding which implies that cyanide is not initially bound to this heme center. It appears that preparations of oxidized CcO contain small but variable amounts of the peroxy form. The variable content of this form is probably responsible for the different response of oxidized oxidase to low concentrations of cyanide [Berka, V., Vygodina, T., Musatov, A., Nicholls, P., & Konstantinov, A. A. (1993) FEBS Lett. 315, 237-241] and may explain the biphasic reduction of the binuclear center with dithionite [Cooper, C. E., Junemann, S., Ioannidis, N., & Wrigglesworth, J. M. (1993) Biochim. Biophys. Acta 1144, 149-160].
通过光谱学和停流法研究了细胞色素c氧化酶的过氧化物衍生物与氰化物的相互作用。在过氧细胞色素氧化酶向其氰化物复合物的转化过程中发现了两个反应。第一个反应的特征是607nm波段的消失、655nm处吸光度的增加以及由于Soret波段蓝移导致的432nm处吸光度的降低；该反应的双分子速率常数约为90 M-1 s-1。第二个反应表现为585和432nm处吸光度的增加；后者是由于Soret波段的红移。第二个过程的速率常数约为22 M-1 s-1。两个反应速率在5至100 mM的氰化物浓度范围内均与氰化物浓度呈线性相关。在第一个反应完成时655nm波段的重新出现表明细胞色素a3暂时变为高自旋，这一发现意味着氰化物最初并非结合在该血红素中心。似乎氧化型细胞色素c氧化酶制剂中含有少量但可变的过氧形式。这种形式的可变含量可能是氧化酶对低浓度氰化物有不同反应的原因[Berka, V., Vygodina, T., Musatov, A., Nicholls, P., & Konstantinov, A. A. (1993) FEBS Lett. 315, 237 - 241]，并且可能解释了用连二亚硫酸盐对双核中心的双相还原[Cooper, C. E., Junemann, S., Ioannidis, N., & Wrigglesworth, J. M. (1993) Biochim. Biophys. Acta 1144, 149 - 160]。
