title: Cyanide inhibition of cytochrome c oxidase. A rapid-freeze e.p.r. investigation.
abstract: 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.
mesh_terms: D001665:Binding Sites; D003300:Copper; D003486:Cyanides / Q000494:pharmacology*; D003574:Cytochrome c Group; D004227:Dithionite; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors*; D005615:Freezing; D010084:Oxidation-Reduction; D011487:Protein Conformation / Q000187:drug effects
chemical_list: D003486:Cyanides; D003574:Cytochrome c Group; D004227:Dithionite; D003300:Copper; D003576:Electron Transport Complex IV