Towards understanding non-equivalence of α and β subunits within human hemoglobin in conformational relaxation and molecular oxygen rebinding.
Abstract
Picosecond to millisecond laser time-resolved transient absorption spectroscopy was used to study molecular oxygen (O2) rebinding and conformational relaxation following O2 photodissociation in the α and β subunits within human hemoglobin in the quaternary R-like structure. Oxy-cyanomet valency hybrids, α2(Fe2+-O2)β2(Fe3+-CN) and α2(Fe3+-CN)β2(Fe2+-O2), were used as models for oxygenated R-state hemoglobin. An extended kinetic model for geminate O2 rebinding in the ferrous hemoglobin subunits, ligand migration between the primary and secondary docking site(s), and nonexponential tertiary relaxation within the R quaternary structure, was introduced and discussed. Significant functional non-equivalence of the α and β subunits in both the geminate O2 rebinding and concomitant structural relaxation was revealed. For the β subunits, the rate constant for the geminate O2 rebinding to the unrelaxed tertiary structure and the tertiary transition rate were found to be greater than the corresponding values for the α subunits. The conformational relaxation following the O2 photodissociation in the α and β subunits was found to decrease the rate constant for the geminate O2 rebinding, this effect being more than one order of magnitude grea...Continue Reading
References
Experimental resolution of cooperative free energies for the ten ligation states of human hemoglobin
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