Effect of cyanide binding on the copper sites of cytochrome c oxidase: an x-ray absorption spectroscopic study

Abstract

Cu x-ray absorption spectroscopy (XAS) has been used to investigate the effect of cyanide treatment on the structures of the copper sites in beef heart cytochrome c oxidase. The Cu K-edge spectrum changes significantly upon cyanide binding to resting state enzyme, as does the Cu extended x-ray absorption fine structure (EXAFS) spectrum. The Cu EXAFS Fourier transfer (FT) exhibits an enhanced peak for the cyanide-treated enzyme in the region containing the Cu ... Fe peak in the resting state FT (at R ' ≈ 2.6–2.7 Å ). This peak in the cyanide-treated sample is hypothesized to arise from “outer shell” scattering from a linear Cu-cyanide moiety, suggesting cyanide binding to cub only (Cu B 2+-CN -) or cyanide bridging between the Fe of heme a 3 and cu B (Fe 3+-(CN-)-Cu B 2+)