title: The nature of haem a3 in the oxidized state of cytochrome c oxidase. Evidence from low-temperature magnetic-circular-dichroism spectroscopy in the near infrared region.
abstract: The magnetic-circular-dichroism (m.c.d.) spectra of oxidized 'resting' bovine cytochrome c oxidase and the cyanide-inhibited form are reported at 5.15 T and at 4.2 K along with m.c.d. magnetization curves plotted at selected wavelengths. In both spectra there are features at 790nm and 1564nm due to Cua and haem a respectively, the e.p.r.-detectable components of the enzyme. There is a new peak at 1946nm only in the spectrum of the cyanide-inhibited enzyme. Arguments are advanced that assign this to low-spin ferric haem a3 bridged to Cua3, thereby forming a ferromagnetically coupled pair of metal ions.
mesh_terms: D002942:Circular Dichroism; D003080:Cold Temperature; D003486:Cyanides / Q000494:pharmacology; D003576:Electron Transport Complex IV / Q000032:analysis* / Q000037:antagonists & inhibitors; D006418:Heme / Q000032:analysis*; D010084:Oxidation-Reduction; D013055:Spectrophotometry, Infrared
chemical_list: D003486:Cyanides; D006418:Heme; D003576:Electron Transport Complex IV