The reaction of cytochrome aa3 with (porphyrin) cytochrome c as studied by pulse radiolysis |
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Authors: | ECI Veerman JW Van Leeuwen KJH Van Buuren BF Van Gelder |
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Institution: | 1. Department of Molecular Biophysics, Physics Laboratory, University of Utrecht, Princetonplein 5, 3584 CC Utrecht The Netherlands;2. Laboratory of Biochemistry, B.C.P. Jansen Institute, University of Amsterdam, Plantage Muidergracht 12, 1018 TV Amsterdam The Netherlands |
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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 2·107 M?1·s?1 (5 mM potassium phosphate, 0.5% Tween 20, pH 7.0, 20°C). (2) The ionic strength dependence of the cytochrome c-cytochromeaa3 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 (?) of the reaction medium on the reaction of cytochrome c with cytochrome aa3 was investigated. With increasing ? the second-order rate constant decreased. |
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Keywords: | Cytochrome c Dielectric constant Hydrated electron Pulse radiolysis |
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