Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 265 (14), 7945-58

Infrared Evidence of Cyanide Binding to Iron and Copper Sites in Bovine Heart Cytochrome C Oxidase. Implications Regarding Oxygen Reduction

Affiliations
  • PMID: 2159465

Infrared Evidence of Cyanide Binding to Iron and Copper Sites in Bovine Heart Cytochrome C Oxidase. Implications Regarding Oxygen Reduction

S Yoshikawa et al. J Biol Chem.

Abstract

Cyanide binding to bovine heart cytochrome c oxidase at five redox levels has been investigated by use of infrared and visible-Soret spectra. A C-N stretch band permits identification of the metal ion to which the CN- is bound and the oxidation state of the metal. Non-intrinsic Cu, if present, is detected as a cyanide complex. Bands can be assigned to Cu+CN at 2093 cm-1, Cu2+CN at 2151 or 2165 cm-1, Fe3+CN at 2131 cm-1, and Fe2+CN at 2058 cm-1. Fe2+CN is found only when the enzyme is fully reduced whereas the reduced Cu+CN occurs in 2-, 3-, and 4-electron reduced species. A band for Fe3+CN is not found for the complex of fully oxidized enzyme but is for all partially reduced species. Cu2+CN occurs in both fully oxidized and 1-electron-reduced oxidase. CO displaces the CN- at Fe2+ to give a C-O band at 1963.5 cm-1 but does not displace the CN- at Cu+. Another metal site, noted by a band at 2042 cm-1, is accessible only in fully reduced enzyme and may represent Zn2+ or another Cu+. Binding of either CN- or CO may induce electron redistribution among metal centers. The extraordinary narrowness of ligand infrared bands indicates very little mobility of the components that line the O2 reduction site, a property of potential advantage for enzyme catalysis. The infrared evidence that CN- can bind to both Fe and Cu supports the possibility of an O2 reduction mechanism in which an intermediate with a mu-peroxo bridge between Fe and Cu is formed. On the other hand, the apparent independence of Fe and Cu ligand-binding sites makes a heme hydroperoxide (Fe-O-O-H) intermediate an attractive alternative to the formation an Fe-O-O-Cu linkage.

Similar articles

See all similar articles

Cited by 12 PubMed Central articles

See all "Cited by" articles

Publication types

Feedback