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Self-exchange rates and electron transfer kinetics of horse heart ferricytochromeCwith amino acid-pentacyanoferrate(II) complexes

Authors
Journal
Journal of Inorganic Biochemistry
0162-0134
Publisher
Elsevier
Publication Date
Volume
20
Issue
1
Identifiers
DOI: 10.1016/0162-0134(84)80005-7
Disciplines
  • Biology

Abstract

Abstract The electron transfer reactions of horse heart cytochrome c with a series of amino acid-pentacyanoferrate(II) complexes have been studied by the stopped-flow technique, at 25°C, μ = 0.100, pH 7 (phosphate buffer). A second-order behavior was observed in the case of the Fe(CN) 5 (histidine) 3− complex, with k = 2.8 x 10 5 M −1 sec −1. For the Fe(CN) 5 (alanine) 4− and Fe(CN) 5(L-glutamate) 5− complexes, only a minor deviation of the second-order behavior, close to the experimental error (k = 3.2 × 10 5 and 1.6 x 10 5 M −1 sec −1, respectively) was noted at high concentrations of the reactants (e.g., 6 × 10 −4 M). The results are in accord with recent work on the Fe(CN) 6 4−/cytochrome c system demonstrating weak association of the reactants. The calculated self-exchange rate constants including electrostatic interactions for the imidazole,L -histidine, 4-aminopyridine, glycinate, β-alaninate, andL-glutamate pentacyanoferrate(II) complexes were 3.3 × 105, 3.3 × 10 5, 2.8 × 10 6,4.1 × 10 2,5.5 × 10 2, and 6.0 M −1 sec −1, respectively. Marcus theory calculations for the cytochrome c reactions were interpreted in terms of two nonequivalent binding sites for the complexes, with the metalloprotein self-exchange rate constants varying from 10 4 M −1 sec −1 (histidine, imidazole, and 4-aminopyridine complexes) to 10 6 M −1 sec −1 (glycinate, β-alaninate, and L-glutamate complexes).

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