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Compound ES of dehaloperoxidase decays via two alternative pathways depending on the conformation of the distal histidine

Thompson, MK and Franzen, S and Ghiladi, RA and Reeder, BJ and Svistunenko, DA (2010) 'Compound ES of dehaloperoxidase decays via two alternative pathways depending on the conformation of the distal histidine.' Journal of the American Chemical Society, 132 (49). 17501 - 17510. ISSN 0002-7863

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Abstract

Dehaloperoxidase (DHP) is a respiratory hemoglobin (Hb) that has been shown to catalyze the conversion of trihalophenols to dihaloquinones in the presence of hydrogen peroxide. Ferric heme states of the resting DHP and the free radical intermediates formed under H2O2 treatment were studied by low-temperature electron paramagnetic resonance spectroscopy in the range of reaction times from 50 ms to 2 min at three different pH values. Two high-spin ferric heme forms were identified in the resting enzyme and assigned to the open and closed conformations of the distal histidine, His55. Two free radicals were found in DHP activated by H2O2: the radical associated with Compound ES (the enzyme with the heme in the oxoferryl state and a radical on the polypeptide chain) has been assigned to Tyr34, and the other radical has been assigned to Tyr38. The Tyr34 radical is formed with a very high relative yield (almost 100% of heme), atypical of other globins. High-performance liquid chromatography analysis of the reaction products showed a pH-dependent formation of covalent heme-to-protein cross-links. The stable DHP Compound RH, formed under H2O2 in the absence of the trihalophenol substrates, is proposed to be a state with the ferric heme covalently cross-linked to Tyr34. A kinetic model of the experimental data suggests that formation of Compound RH and formation of the Tyr38 radical are two alternative routes of Compound ES decay. Which route is taken depends on the conformation of His55: in the less populated closed conformation, the Tyr38 radical is formed, but in the major open conformation, Compound ES decays, yielding Compound RH, a product of safe termination of the two oxidizing equivalents of H2O2 when no substrate is available. © 2010 American Chemical Society.

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 10:54
Last Modified: 23 Aug 2019 17:15
URI: http://repository.essex.ac.uk/id/eprint/921

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