title: The reaction of cytochrome aa3 with (porphyrin) cytochrome c as studied by pulse radiolysis.
abstract: (1) Using the pulse-radiolysis and stopped-flow techniques, the reactions of iron-free (porphyrin) cytochrome c and native cytochrome c with cytochrome aa3 were investigated. The porphyrin cytochrome c anion radical (generated by reduction of porphyrin cytochrome c by the hydrated electron) can transfer its electron to cytochrome aa3. The bimolecular rate constant for this reaction is 2 x 10(7) M-1 . s-1 (5 mM potassium phosphate, 0.5% Tween 20, pH 7.0, 20 degrees C). (2) The ionic strength dependence of the cytochrome c-cytochrome aa3 interaction was measured in the ionic strength range between 40 and 120 mM. At ionic strengths below 30 mM, a cytochrome c-cytochrome aa3 complex is formed in which cytochrome c is no longer reducible by the hydrated electron. A method is described by which the contributions of electrostatic forces to the reaction rate can be determined. (3) Using the stopped-flow technique, the effect of the dielectric constant (epsilon) of the reaction medium on the reaction of cytochrome C with cytochrome aa3 was investigated. With increasing epsilon the second-order rate constant decreased.
mesh_terms: D000818:Animals; D002417:Cattle; D003574:Cytochrome c Group / Q000378:metabolism*; D004563:Electrochemistry; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006736:Horses; D007700:Kinetics; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D011166:Porphyrins / Q000378:metabolism; D011675:Pulse Radiolysis
chemical_list: D003574:Cytochrome c Group; D011166:Porphyrins; D006418:Heme; D003576:Electron Transport Complex IV