Cyanide inhibition of cytochrome c oxidase. A rapid-freeze e.p.r. investigation

Biochem J. 1984 Dec 15;224(3):829-37. doi: 10.1042/bj2240829.


The inhibition of cytochrome c oxidase by cyanide, starting either with the resting or the pulsed enzyme, was studied by rapid-freeze quenching followed by quantitative e.p.r. It is found that a partial reduction of cytochrome oxidase by transfer of 2 electron equivalents from ferrocytochrome c to cytochrome a and CuA will induce a transition from a closed to an open enzyme conformation, rendering the cytochrome a3-CuB site accessible for cyanide binding, possibly as a bridging ligand. A heterogeneity in the enzyme is observed in that an e.p.r. signal from the cytochrome a3 3+-HCN complex is only found in 20% of the molecules, whereas the remaining cyanide-bound a3-CuB sites are e.p.r.-silent.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Copper
  • Cyanides / pharmacology*
  • Cytochrome c Group
  • Dithionite
  • Electron Spin Resonance Spectroscopy
  • Electron Transport Complex IV / antagonists & inhibitors*
  • Freezing
  • Oxidation-Reduction
  • Protein Conformation / drug effects


  • Cyanides
  • Cytochrome c Group
  • Dithionite
  • Copper
  • Electron Transport Complex IV