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Tyrosine as a redox-active center in electron transfer to ferryl heme in globins

Reeder, BJ and Cutruzzola, F and Bigotti, MG and Hider, RC and Wilson, MT (2008) 'Tyrosine as a redox-active center in electron transfer to ferryl heme in globins.' Free Radical Biology and Medicine, 44 (3). 274 - 283. ISSN 0891-5849

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Abstract

A wide range of organic reductants, including many iron chelators, reduce ferryl myoglobin to its ferric states in exponential time courses whose rate constants display double hyperbolic dependencies on the reductant concentration. This concentration dependence is consistent with a mechanism in which electron transfer to the heme takes place at two independent sites where reductants appear to bind. We propose that the low-affinity site is located close to the heme edge, within the heme pocket; the maximum rate of electron transfer is highly variable depending on the nature of the reductant (0.005 to > 10 s- 1). The other site has higher apparent affinity (KD 0.2-50 μM) but a low maximum rate of electron transfer (0.005 to 0.01 s- 1). By examining native and engineered proteins we have determined that the high-affinity pathway represents a through-protein electron transfer pathway that involves a specific tyrosine residue. The low apparent rate constant for electron transfer from the tyrosine to the heme (∼ 5 Å) is accounted for by proposing that electron transfer occurs only in a very poorly populated protonated state of ferryl heme and tyrosine. Hemoglobin shows similar kinetics but only one subunit exhibits double rectangular hyperbolic concentration dependency. The consequence of a high-affinity through-protein electron transfer pathway to the cytotoxicity of ferryl heme is discussed. © 2007 Elsevier Inc. All rights reserved.

Item Type: Article
Subjects: Q Science > QH Natural history > QH301 Biology
Divisions: Faculty of Science and Health > Life Sciences, School of
Depositing User: Jim Jamieson
Date Deposited: 07 Oct 2011 10:58
Last Modified: 14 Aug 2019 10:15
URI: http://repository.essex.ac.uk/id/eprint/924

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