Kinetics of oxygen binding and subunit assembly for the hemoglobin alpha subunit.
A thorough kinetic characterization of the O2-binding and self-association reactions of alpha-subunits of human hemoglobin A has been performed. All of the rate constants for a five step reaction model linking the monomer-dimer reaction to the O2-binding steps have been determined for the first time. Our analysis of the ligand binding reaction shows that both monomer and dimer have nearly identical intrinsic O2-association and dissociation rate constants and therefore identical affinities for oxygen. During this investigation we discovered a small absorbance difference between the oxy-monomer and oxy-dimer alpha-subunits. This difference spectrum enabled direct measurements of the alpha O2 self-association reaction. We find an association rate constant of, 2.0 10(5) M(-1)s-1, similar to that for other subunit assembly processes in the hemoglobin system. Our results also suggest that the deoxy-subunit assembly kinetics must be similar to that for the oxy-subunit. These kinetic results together with the equilibrium constants obtained for these solution conditions by Ackers and coworkers provides, for the first time, a complete kinetic and thermodynamic description of all the intrinsic ligand binding and association reactions for alpha-subunits.
Windsor
W T
WT
Department of Molecular and Cell Biology, University of Connecticut, Storrs 06268.
Philo
J S
JS
Potschka
M
M
Schuster
T M
TM
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006441:Hemoglobin A / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D010100:Oxygen / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics
D008024:Ligands; D006441:Hemoglobin A; D010100:Oxygen