The reaction of cyanide with peroxidatic forms of cytochrome oxidase

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Abstract
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].

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