Electron exchange in models for heme proteins

Dixon, Dabney W.; Barbush, Michael; Shirazi, Ataollah

doi:10.1021/ja00328a068

Cited by 19 publications

(9 citation statements)

References 4 publications

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“…Because electron transfer is thought to fall off exponentially with distance, increased heme exposure should result in a faster electron transfer rate constant. Indeed, as we (Dixon et al, 1984;Shirazi et al, 1985), and others (Moore et al, 1984) have observed, small cytochromes c do have faster self-exchange rate constants than the larger proteins. However, for c and C551, the heme exposure (i.e., the percent of the surface of the protein that is heme) is very similar.…”

Section: Steric Considerationssupporting

confidence: 65%

“…Cytochromes c and b5 have much slower rate constants for electron self-exchange than does cytochrome c551. Although the heme of cytochrome c551 is more exposed than that of horse heart cytochrome c (Stellwagen, 1978;Dixon et al, 1984), a quantitative analysis shows that the difference in rate constants is not due primarily to this difference in heme exposure.…”

Section: Introductionmentioning

confidence: 92%

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Electrostatic and steric control of electron self-exchange in cytochromes c, c551, and b5

Dixon

Hong

Woehler

1989

Biophysical Journal

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The ionic strength dependence of the electron self-exchange rate constants of cytochromes c, c551, and b5 has been analyzed in terms of a monopole-dipole formalism (van Leeuwen, J.W. 1983. Biochim. Biophys. Acta. 743:408-421). The dipole moments of the reduced and oxidized forms of Ps. aeruginosa cytochrome c551 are 190 and 210 D, respectively (calculated from the crystal structure). The projections of these on the vector from the center of mass through the exposed heme edge are 120 and 150 D. For cytochrome b5, the dipole moments calculated from the crystal structure are 500 and 460 D for the reduced and oxidized protein; the projections of these dipole moments through the exposed heme edge are -330 and -280 D. A fit of the ionic strength dependence of the electron self-exchange rate constants gives -280 (reduced) and -250 (oxidized) D for the center of mass to heme edge vector. The self-exchange rate constants extrapolated to infinite ionic strength of cytochrome c, c551, and b5 are 5.1 x 10(5), 2 x 10(7), and 3.7 x 10(5) M-1 s-1, respectively. The extension of the monopole-dipole approach to other cytochrome-cytochrome electron transfer reactions is discussed. The control of electron transfer by the size and shape of the protein is investigated using a model which accounts for the distance of the heme from each of the surface atoms of the protein. These calculations indicate that the difference between the electrostatically corrected self-exchange rate constants of cytochromes c and c551 is due only in part to the different sizes and heme exposures of the two proteins.

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Section: Steric Considerationssupporting

confidence: 65%

Section: Introductionmentioning

confidence: 92%

Electrostatic and steric control of electron self-exchange in cytochromes c, c551, and b5

Dixon

Hong

Woehler

1989

Biophysical Journal

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“…[193]. The rate constant k for heme-heme self-exchange is 1 • 106-1 • 101° M -1-s -1 depending on the nature of the axial ligands (through their effect on hi and ~'o) and the medium [205]. The value of ~,o/4 for heme exchange will depend on the nature of the solvent, but is expected to be small because of the relatively large size of the heme group.…”

Section: Ib)mentioning

confidence: 99%

Electron transfers in chemistry and biology

Marcus

Sutin

1985

Biochimica et Biophysica Acta (BBA) - Reviews on Bioenergetics

8,297

230

7,865

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“…Self-exchange rate constants for many redox reactions of metalloporphyrins have been determined in this manner, especially for the metal-centered redox couples. 3 For example, electron self-exchange rate constants for tetraarylporphyrin complexes fall in the range 10 7 to 10 8 M −1 s −1 for the Fe 2+/3+ complexes, [6][7][8][9] and 10 −3 to 10 4 M −1 s −1 for the Co 2+/3+ complexes. 10,11 On the contrary, the porphyrin-centered redox reactions have been scarcely studied, 12 partly because of the highly reactive nature of this type of reaction: smaller inner-sphere reorganization energies are required for this type of reaction compared with the metal-centered redox reactions, as the latter type of reactions generally involve a large change in the metal-nitrogen bond lengths that pushes up the inner-sphere activation barrier.…”

Section: Introductionmentioning

confidence: 99%

Electron transfer reactions between copper(ii) porphyrin complexes and various oxidizing reagents in acetonitrileElectronic supplementary information (ESI) available: Figures reporting the UV-visible absorption spectra of [Cu(OEP)] and the product of the reaction of [Cu(OEP)] with Cu(ii) triflate in acetonitrile, the dependence of the absorbance on the ratio of the total concentrations of Cu(ii) ion and [Cu(OEP)] for the reaction of [Cu(OEP)] and Cu(ii) triflate, and the dependence of the pseudo-first-orde

et al. 2004

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Homogeneous electron transfer reactions of the Cu(II) complexes of 5,10,15,20-tetraphenylporphyrin (TPP) and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) with various oxidizing reagents were spectrophotometrically investigated in acetonitrile. The reaction products were confirmed to be the pi-cation radicals of the corresponding Cu(II)-porphyrin complexes on the basis of the electronic spectra and the redox potentials of the complexes. The rate of the electron transfer reaction between the Cu(II)-porphyrin complex and solvated Cu(2+) was determined as a function of the water concentration under the pseudo first-order conditions where Cu(2+) is in large excess over the Cu(II)-porphyrin complex. The decrease in the pseudo first-order rate constant with increasing the water concentration was attributed to the stepwise displacement of acetonitrile in [Cu(AN)(6)](2+)(AN = acetonitrile) by water, and it was concluded that only the Cu(2+) species fully solvated by acetonitrile, [Cu(AN)(6)](2+), possesses sufficiently high redox potential for the oxidation of Cu(ii)-OEP and Cu(ii)-TPP. The reactions of the Cu(II)-porphyrin complexes with other oxidizing reagents such as [Ni(tacn)(2)](3+)(tacn = 1,4,7-triazacyclononane) and [Ru(bpy)(3)](3+)(bpy = 2,2'-bipyridine) were too fast to be followed by a conventional stopped-flow technique. Marcus cross relation for the outer-sphere electron transfer reaction was used to estimate the rate constants of the electron self-exchange reaction between Cu(II)-porphyrin and its pi-cation radical: log(k/M(-1) s(-1))= 9.5 +/- 0.5 for TPP and log(k/M(-1) s(-1))= 11.1 +/- 0.5 for OEP at 25.0 degrees C. Such large electron self-exchange rate constants are typical for the porphyrin-centered redox reactions for which very small inner- and outer-sphere reorganization energies are required.

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Electron exchange in models for heme proteins

Cited by 19 publications

References 4 publications

Electrostatic and steric control of electron self-exchange in cytochromes c, c551, and b5

Electrostatic and steric control of electron self-exchange in cytochromes c, c551, and b5

Electron transfers in chemistry and biology

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