title: Biochemical and biophysical studies on cytochrome c oxidase.  XX. Reaction with sulphide.
abstract: 1. Upon addition of sulphide to oxidized cytochrome c oxidase, a low-spin heme sulphide compound is formed with an EPR signal at gx = 2.54, gy = 2.23 and gz = 1.87.  Concomitantly with the formation of this signal the EPR-detectable low-spin heme signal at g = 3 and the copper signal near g = 2 decrease in intensity, pointing to a partial reduction of the enzyme by sulphide.  2. The addition of sulphide to cytochrome c oxidase, previously reduced in the presence of azide or cyanide, brings about a disappearance of the azido-cytochrome c oxidase signal at gx = 2.9, gy = 2.2, and gz = 1.67 and a decrease of the signal at g = 3.6 of cyano-cytochrome c oxidase.  Concomitantly the sulphide-induced EPR signal is formed.  3. These observations demonstrate that azide, cyanide and sulphide are competitive for an oxidized binding site on cytochrome c oxidase.  Moreover, it is shown that the affinity of cyanide and sulphide for this site is greater than that of azide.
mesh_terms: D000818:Animals; D001386:Azides; D001665:Binding Sites; D002417:Cattle; D003300:Copper / Q000032:analysis; D003486:Cyanides; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000378:metabolism; D006418:Heme / Q000032:analysis; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D011485:Protein Binding; D011487:Protein Conformation; D013440:Sulfides
chemical_list: D001386:Azides; D003486:Cyanides; D013440:Sulfides; D006418:Heme; D003300:Copper; D003576:Electron Transport Complex IV