THE REACTION OF CYANIDE WITH PEROXIDATIC FORMS OF CYTOCHROME-OXIDASE

The interaction of peroxidatic derivatives of cytochrome c oxidase wit h cyanide has been investigated by optical spectroscopy and the stoppe d-flow method. Two reactions were found in the conversion of peroxy cy tochrome oxidase to its cyanide complex. The first reaction is charact erized by the loss of the 607 nm band, an increase in absorbance at 65 5 nm, and a decrease in absorbance at 432 nm resulting from a blue-shi ft of the Soret band; this reaction occurred with a bimolecular rate c onstant 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-sh ift of the Soret band. This second process proceeded with a rate const ant Of about 22 M(-1) s(-1). Both reaction rates are Linearly dependen t on the concentration of cyanide between 5 and 100 mM. The reappearan ce of the 655 nm band at the completion of the first reaction suggests that cytochrome a(3) becomes transiently high-spin, a finding which i mplies that cyanide is not initially bound to this heme center. It app ears that preparations of oxidized CcO contain small but variable amou nts of the peroxy form. The variable content of this form is probably responsible for the different response of oxidized oxidase to low conc entrations of cyanide [Berka, V., Vygodina, T., Musatov, A., Nicholls, P., gt Konstantinov, A. A. (1993) FEES Lett. 315, 237-241] and may ex plain the biphasic reduction of the binuclear center with dithionite [ Cooper, C. E., Junemann, S., Ioannidis, N., and Wrigglesworth, J. M. ( 1993) Biochim. Biophys. Acta 1144, 149-160].