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The βlys66tyr variant of human hemoglobin as a component of a blood substitute

Silkstone, RS and Silkstone, G and Baath, JA and Rajagopal, B and Nicholls, P and Reeder, BJ and Ronda, L and Bulow, L and Cooper, CE (2016) 'The βlys66tyr variant of human hemoglobin as a component of a blood substitute.' Advances in Experimental Medicine and Biology, 876. 455 - 460. ISSN 0065-2598

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Abstract

© Springer Science+Business Media, New York 2016. It has been proposed that introducing tyrosine residues into human hemoglobin (e.g. βPhe41Tyr) may be able to reduce the toxicity of the ferryl heme species in extracellular hemoglobin-based oxygen carriers (HBOC) by facilitating long-range electron transfer from endogenous and exogenous antioxidants. Surface-exposed residues lying close to the solvent exposed heme edge may be good candidates for mutations. We therefore studied the properties of the βLys66Tyr mutation. Hydrogen peroxide (H2O2) was added to generate the ferryl protein. The ferryl state in βLys66Tyr was more rapidly reduced to ferric (met) by ascorbate than recombinant wild type (rwt) or βPhe41Tyr. However, βLys66Tyr suffered more heme and globin damage following H2O2addition as measured by UV/visible spectroscopy and HPLC analysis. βLys66Tyr differed notably from therwt protein in other ways. In the ferrous state the βLys66Tyr forms oxy, CO, and NO bound heme complexes similar torwt. However, the kinetics of CO binding to the mutant was faster thanrwt, suggesting a more open heme crevice. In the ferric (met) form the typical met Hb acid-alkaline transition (H2O to-OH) appeared absent in the mutant protein. A biphasicity of cyanide binding was also evident. Expression in E. coli of the βLys66Tyr mutant was lower than therwt protein, and purification included significant protein heterogeneity. Whilst, βLys66Tyr and rwt autoxidised (oxy to met) at similar rates, the oxygen p50 for βLys66Tyr was very low. Therefore, despite the apparent introduction of a new electron transfer pathway in the βLys66Tyr mutant, the heterogeneity, and susceptibility to oxidative damage argue against this mutant as a suitable starting material for a HBOC.

Item Type: Article
Subjects: Q Science > QP Physiology
Divisions: Faculty of Science and Health > Biological Sciences, School of
Depositing User: Jim Jamieson
Date Deposited: 18 Apr 2016 10:57
Last Modified: 05 Feb 2019 20:15
URI: http://repository.essex.ac.uk/id/eprint/16465

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