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Architecture of Allosteric Structure. Rate Equations, Rate Constants, and Equilibrium Constants for Reaction of: Hb4 with O2 and (HbO2)4 with Dithionate, in the Presence of 2,3-Bisphosphoglycerate
preprintsubmitted on 22.11.2019, 21:15 and posted on 29.11.2019, 18:21 by Francis Knowles, Samantha J. Doyle, Douglas Magde
Three unknown quantities are all that is required to describe the O2-equilibrium binding curve for fractional saturation of human hemoglobin in red blood cells, under standard conditions: Kα, the O2-binding constant of equivalent α-chains; KC, the equilibrium constant for the T →R conformation change; Kβ, the O2-binding constant of equivalent β-chains. The model for formulation of the equation of state is a 3-stage ordered sequence of reactions. The values of were established by determination of rate constants for the oxygenation reaction and the dithionite-mediated de oxygenation reaction. The rate law for the forward reaction in the presence of excess O2 yields The same rate law yields for the dithionite-mediated de-oxygenation reaction. The rate constants for binding O2 are pseudo-first-order. The rate constants for release of O2 are first-order. Reactions involving O2, are 2-step ordered sequences of equivalent subunits. Progress curves for a 2-step ordered sequence of equivalent chains collapse to a first order reaction. Progress curves for both oxygenation and dithionite-mediated de-oxygenation reactions return is 0.0580 for the oxygenation reaction and 0.0358 for the dithionite-mediated de-oxygenation reaction. The corresponding values from the O2-equilibrium binding curve are: and = 0.02602. Values of determined from rate constants of progress curves for oxygenation and dithionite-mediated de-oxygenation reactions are close to values of determined by analysis of the O2-equilibrium binding curves for whole blood, by the Perutz/Adair equation.