Kinetic studies on redox reactions of hemoproteins. I. Reduction of thermoresistant cytochrome c-552 and horse heart cytochrome c by ferrocyanide

doi:10.1016/0005-2728(77)90086-X

Biochimica et Biophysica Acta (BBA) - Bioenergetics

Volume 460, Issue 3, 9 June 1977, Pages 480-489

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Abstract

The oxidation-reduction reaction of horse heart cytochrome c and cytochrome c (552, Thermus thermophilus), which is highly thermoresistant, was studied by temperature-jump method. Ferrohexacyanide was used as reductant.

Thermodynamic and activation parameters of the reaction obtained for both cytochromes were compared with each other. The results of this showed that (1) the redox potential of cytochrome c-552,+0.19 V, is markedly less than that of horse heart cytochrome c. (2) ▵H_ox^‡ of cytochrome c-552 is considerably lower than that of horse heart cytochrome c. (3) ▵H_ox^‡ and ▵S_red^‡ of cytoochrome c-552 are more negative than those of horse heart cytochrome c. (4) k_red of cytochrome c-552 is much lower than that of horse heart cytochrome c at room temperature.

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The reduction of horse and Candida krusei cytochromes c by ferrocyanide has been studied by ¹H NMR spectroscopy and the reaction found to involve a precursor complex of ferrocyanide bound to ferricytochrome c (pH^* 7.4, ²H₂O, I = 0.12, and 25°C). The electron transfer rate constants for the reduction of the two ferricytochromes by associated ferrocyanide were found to be the same at 780 ± 80 sec^-1 but the association constants for binding of ferrocyanide to ferricytochrome c were significantly different: horse, 90 ± 20 M⁻¹ and Candida, 285 ± 30 M⁻¹. The different association constants partly accounts for the previously observed reactivity difference between horse and Candida cytochromes c. Comparison of the NMR data with data obtained by other kinetic methods has allowed the electron transfer rate constant for the oxidation of ferrocytochrome c by associated ferricyanide to be determined. This was found to be 4.6 ± 1 × 10⁴ sec⁻¹.
Metal-mediated reduction of cytochrome c by thioglycolic acid
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The reduction of cytochrome c by thioglycolic acid was found to be extremely sensitive to metal catalysis. The rate of the uncatalyzed reaction was negligible in comparison with rates obtained from reactions supplemented with catalytic amounts of copper or iron. Both the catalyzed and uncatalyzed reactions were independent of pH (near neutrality) but when o-phenanthroline was included in the reaction mixture, a pH dependence was induced. This pH dependence is the result of an interference of oxygen with the metal complexes. A comparison of the rate constants at zero ionic strenght, which were obtained from the application of the Debye-Hückel theory for the ionic strength dependence, demonstrated that copper complexes are superior catalysts as compared with iron complexes. Our results suggest that in the copper-mediated reaction, the catalyst is a cupric thioglycolate complex with a net charge of −2. The addition of o-phenanthroline to the reaction mixture results in a tenfold decrease in the catalytic activity and in a change in the net charge of the catalyst to −1. At pH 8 the iron-mediated reduction is catalyzed by a ferric thioglycolate complex, whereas at pH 7 a ferrothioglycolate complex provides the catalytic activity. Both complexes have a net negative charge of −2. At both pH's the catalytic activity is completely abolished by the addition of o-phenanthroline. The results demonstrate the effectiveness by which metal-sulfur complexes can facilitate one-electron transfer reactions and could there-fore serve as a model in the study of various biological oxidations.
Comparison of the redox reactions of various types of cytochrome c with iron hexacyanides
1981, BBA - Bioenergetics
The dynamic behavior of various types of cytochromes c in the redox reaction with iron hexacyanides was studied using a temperature-jump method in order to elucidate the molecular mechanism of the redox reaction of cytochromes with their oxidoreductants.
Transmittance after the temperature jump changed through a single exponential decay for all cytochromes investigated.
Under a constant concentration of anion, the redox reaction of various types of cytochrome c with iron hexacyanides was analyzed according to the scheme: where C(III) and C(II) are ferric and ferrous cytochromes, respectively, Fe(III) and Fe(II) are ferri- and ferrocyanides, respectively, C(III) · Fe(II) is the ferricytochrome-ferrocyanide complex and C(II) · Fe(III) is the ferrocytochrome-ferricyanide complex. When step B is slower than the other two steps A and C, τ⁻¹ can be represented approximately as where the bar over the variables denotes the equilibrium value. In a large excess of ferrocyanide against cytochrome, we can estimate k₂, k₋₂, K₁ and K₃ independently. In the case of horse cytochrome c at 18°C in 0.1 M phosphate buffer at pH 7 with 0.3 M KNO₃, the estimated parameters are k₂ = 100 ± 50 s⁻¹, k₋₂ = (3.5 ± 1.0) · 10³ s⁻¹, K₁ = 15 ± 7 M⁻¹ and K₃ = (8.5 ± 1.5) · 10⁻⁴ M. From the same experiments for seven cytochromes (cytochrome c from horse, tuna, Candida krusei, Saccharomyces oviformis, Rhodospirillum rubrum cytochrome c₂, Spirulina platensis cytochrome c-554 and Thermus thermophilus cytochrome c-552), the following results can be deduced. (1) Each parameter defined in the scheme above (k₂, k₋₂, K₁, K₃) diverged beyond the error range. Above all, k₂ values of cytochromes c-554 and c-552 are as large as 1 · 10⁴ s⁻¹ and much larger than those for the other cytochromes (to 50 approx. 700 S⁻¹). (2) The variance of k₂K₁ and k₋₂/K₃ are relatively less than the variances of individual parameters (k₂, k₋₂, K₁ and K₃), which suggests that the values of k₂K₁ and k₋₂/K₃ have been conserved during the course of evolution.
Oxidation of heme proteins by copper(II) complexes. Rates and mechanism of the copper catalysed autoxidation of cytochrome c, myoglobin and hemoglobin
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The mechanism of the autoxidation of ferrocytochrome c catalysed by some copper(II) complexes has been estblished. In most cases the rate determining step was found to be the one electron oxidation of the cytochrome by the copper(II) species, which was followed by the rapid reoxidation of the resulting Cu(I) complexes by molecular oxygen. The rate constants for the electron transfer reactions of several copper(II) complexes with ferrocytochrome c, myoglobin and hemoglobin have been measured at 25 °C. It was shown that these rates for the copper complexes, as well as those for several other oxidants, are consistent with simple outer sphere electron transfer through the heme edge for all the heme proteins. the redox potential of the reacting species was found to be the dominant factor in determining the relative rate of the electron transfer reactions. This enables the catalytic activity of different copper complexes to be predicted.
Reduction of horse heart ferricytochrome c by glutathione: Evidence for two different conformational forms of ferricytochrome c in neutral and slightly alkaline solutions
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Kinetic studies on redox reactions of hemoproteins. I. Reduction of thermoresistant cytochrome c-552 and horse heart cytochrome c by ferrocyanide

Abstract

Biochim. Biophys. Acta

J. Biol. Chem.

J. Mol. Biol.

J. Biol. Chem.

J. Biol. Chem.

Seikagaku

Int. J. System. Bacteriol.