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Direct measurements of intramolecular electron transfer rates between cytochrome c and cytochrome c peroxidase: effects of exothermicity and primary sequence on rate.

Title:

Direct measurements of intramolecular electron transfer rates between cytochrome c and cytochrome c peroxidase: effects of exothermicity and primary sequence on rate.

Cheung, E., Taylor, K., Kornblatt, Jack A. ORCID: https://orcid.org/0000-0002-9802-8321, English, Ann M. ORCID: https://orcid.org/0000-0002-3696-7710, McLendon, G. and Miller, J. R. (1986) Direct measurements of intramolecular electron transfer rates between cytochrome c and cytochrome c peroxidase: effects of exothermicity and primary sequence on rate. Proceedings of the National Academy of Sciences, 83 (5). pp. 1330-1333. ISSN 0027-8424

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Official URL: https://doi.org/10.1073/pnas.83.5.1330

Abstract

Rapid mixing of ferrocytochrome c peroxidase [cyt c peroxidase(II)] and ferricytochrome c [cyt c(III)] results in the reduction of cyt c(III) by cyt c peroxidase(II). In 10 mM phosphate, pH 7.0, the rate of decay of cyt c peroxidase(II) and the rate of accumulation of cyt c(II) give equal first-order rate constants: k = 0.23 +/- 0.02 s-1. Equivalent results are obtained by pulse radiolysis using isopropanol radical as the reducing agent. This rate is independent of the initial cyt c(III):cyt c peroxidase(II) ratios. These results are consistent with unimolecular electron transfer occurring within a cyt c(III)-cyt c peroxidase(II) complex. When cyt c is replaced by porphyrin cyt c (iron-free cyt c), a complex still forms with cyt c peroxidase. On radiolysis, using e-aq as the reducing agent, intracomplex electron transfer occurs from the porphyrin cyt c anion radical to cyt c peroxidase(III) with k = 150 s-1. This large rate increase with increasing delta G degrees suggests that the barrier for intracomplex electron transfer is large. Finally, we have briefly investigated how the cyt c peroxidase(II)----cyt c(III) rate depends on the primary structure of cyt c(III). We find the reactivity order to be as follows: yeast (k = 3.4 s-1) greater than horse (k = 0.3 s-1) greater than tuna (k = 0.2 s-1). These results mirror a report [Ho, P. S., Sutoris, C., Liang, N., Margoliash, E. & Hoffman, B. M. (1985) J. Am. Chem. Soc. 107, 1070-1071] on excited state reactions of the cyt c/cyt c peroxidase couple.

Divisions:Concordia University > Faculty of Arts and Science > Chemistry and Biochemistry
Item Type:Article
Refereed:Yes
Authors:Cheung, E. and Taylor, K. and Kornblatt, Jack A. and English, Ann M. and McLendon, G. and Miller, J. R.
Journal or Publication:Proceedings of the National Academy of Sciences
Date:March 1986
Digital Object Identifier (DOI):10.1073/pnas.83.5.1330
ID Code:985185
Deposited By: MIA MASSICOTTE
Deposited On:28 May 2019 14:00
Last Modified:29 May 2019 13:35

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