title: Studies on the heme environment of horse heart ferric cytochrome c. Azide and imidazole complexes of ferric cytochrome c.
abstract: Horse heart ferric cytochrome c was investigated by the following three methods: (I) Light absorption spectrophotometry at 23 degrees C and 77 degrees K; (II) Electron paramagnetic resonance (EPR) spectroscopy at 20 degrees K; (III) Precise equilibrium measurements of ferric cytochrome c with azide and imidazole between 14.43 and 30.90 degrees C. I and II have demonstrated that: (1) Ferric cytochrome c azide and imidazole complexes were in the purely low spin state between 20 degrees K and 23 degrees C; (2) The energy for the three t2g orbitals calculated in one hole formalism shows that azide or imidazole bind to the heme iron in a similar manner to met-hemoglobin azide or imidazole complexes, respectively. III has demonstrated that: (1) The change of standard enthalpy and that of standard entropy were -2.3 kcal/mol and -1.6 cal/mol per degree for the azide complex formation, and -1.4 kcal/mol and 2.9 cal/mol per degree for the imidazole complex formation. (2) A linear relationship between the change of entropy and that of enthalpy was observed for the above data for the cyanide complex formation. The complex formation of ferric cytochrome c was discussed based on the results of X-ray crystallographic studies compared with hemoglobin and myoglobin.
mesh_terms: D000818:Animals; D001386:Azides; D055598:Chemical Phenomena; D002621:Chemistry; D003574:Cytochrome c Group; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme; D006454:Hemoglobins; D006736:Horses; D007093:Imidazoles; D007501:Iron; D007700:Kinetics; D008024:Ligands; D009206:Myocardium / Q000201:enzymology; D009211:Myoglobin; D013053:Spectrophotometry; D013696:Temperature; D013816:Thermodynamics
chemical_list: D001386:Azides; D003574:Cytochrome c Group; D006454:Hemoglobins; D007093:Imidazoles; D008024:Ligands; D009211:Myoglobin; D006418:Heme; D007501:Iron