The βLys66Tyr Variant of Human Hemoglobin as a Component of a Blood Substitute

Advances in Experimental Medicine and Biology
R S SilkstoneChris E Cooper

Abstract

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 H2O2 addition as measured by UV/visible spectroscopy and HPLC analysis. βLys66Tyr differed notably from the rwt protein in other ways. In the ferrous state the βLys66Tyr forms oxy, CO, and NO bound heme complexes similar to rwt. However, the kinetics of CO binding to the mutant was faster than rwt, 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. ...Continue Reading

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