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Haptoglobin binding stabilizes hemoglobin ferryl iron and the globin radical on tyrosine β145

Cooper, CE and Schaer, DJ and Buehler, PW and Wilson, MT and Reeder, BJ and Silkstone, G and Svistunenko, DA and Bulow, L and Alayash, AI (2013) 'Haptoglobin binding stabilizes hemoglobin ferryl iron and the globin radical on tyrosine β145.' Antioxidants and Redox Signaling, 18 (17). 2264 - 2273. ISSN 1523-0864

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Abstract

Aim: Hemoglobin (Hb) becomes toxic when released from the erythrocyte. The acute phase protein haptoglobin (Hp) binds avidly to Hb and decreases oxidative damage to Hb itself and to the surrounding proteins and lipids. However, the molecular mechanism underpinning Hp protection is to date unclear. The aim of this study was to use electron paramagnetic resonance (EPR) spectroscopy, stopped flow optical spectrophotometry, and site-directed mutagenesis to explore the mechanism and specifically the role of specific tyrosine residues in this protection. Results: Following peroxide challenge Hb produces reactive oxidative intermediates in the form of ferryl heme and globin free radicals. Hp binding increases the steady state level of ferryl formation during Hb-catalyzed lipid peroxidation, while at the same time dramatically inhibiting the overall reaction rate. This enhanced ferryl stability is also seen in the absence of lipids and in the presence of external reductants. Hp binding is not accompanied by a decrease in the pK of ferryl protonation; the protonated ferryl species still forms, but is intrinsically less reactive. Ferryl stabilization is accompanied by a significant increase in the concentration of the peroxide-induced tyrosine free radical. EPR spectral parameters and mutagenesis studies suggest that this radical is located on tyrosine 145, the penultimate C-terminal amino acid on the beta Hb subunit. Innovation: Hp binding decreases both the ferryl iron and free radical reactivity of Hb. Conclusion: Hp protects against Hb-induced damage in the vasculature, not by preventing the primary reactivity of heme oxidants, but by rendering the resultant protein products less damaging. Antioxid. Redox Signal. 18, 2264-2273. © 2013, Mary Ann Liebert, Inc.

Item Type: Article
Subjects: Q Science > QH Natural history > QH301 Biology
Divisions: Faculty of Science and Health > Life Sciences, School of
Depositing User: Users 161 not found.
Date Deposited: 20 Dec 2014 22:11
Last Modified: 09 Aug 2019 17:15
URI: http://repository.essex.ac.uk/id/eprint/10199

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