title: Low temperature magnetic circular dichroism spectra and magnetization properties of extracted heme a3+ bis-imidazole. A model of cytochrome a in bovine cytochrome c oxidase.
abstract: Heme a3+ isolated from bovine cardiac muscle cytochrome oxidase has been converted to the bis-imidazole species and studied by magnetic circular dichroism (MCD) spectroscopy. Spectra have been recorded down to 1.5 degrees K, enabling the MCD magnetization curves to be measured at a number of wavelengths in the visible and near infrared regions. The experimentally determined curves show excellent correlation to a curve using the g-values determined by electron paramagnetic resonance spectroscopy to be gz = 2.96, gy = 2.29, and gx = 1.73. The data show that the bis-imidazole derivative of extracted heme a3+ is an excellent model of cytochrome a in the enzyme, confirming the presence of two histidine residues in the protein as the fifth and sixth ligands. The spectral features of heme a3+ bis-imidazole in the near infrared region are consistent with transitions of the porphyrin ( a1u , a2u ) to ferric (eg) charge transfer type.
mesh_terms: D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002942:Circular Dichroism / Q000379:methods; D017936:Cytochrome a Group; D003580:Cytochromes / Q000032:analysis*; D003576:Electron Transport Complex IV / Q000032:analysis*; D006418:Heme / Q000031:analogs & derivatives* / Q000032:analysis; D006639:Histidine / Q000032:analysis; D007093:Imidazoles / Q000032:analysis*; D008954:Models, Biological; D009132:Muscles / Q000201:enzymology
chemical_list: D017936:Cytochrome a Group; D003580:Cytochromes; D007093:Imidazoles; D006418:Heme; D006639:Histidine; C041631:heme a3 bis-imidazole; D003576:Electron Transport Complex IV