Description of hemoglobin oxygenation under universal solution conditions by a global allostery model with a single adjustable parameter

The Monod-Wyman-Changeux allosteric model parameters evaluated from accurate oxygen equilibrium curves (OECs) of hemoglobin that were measured in an extremely wide range of structural constraints, imposed by allosteric effectors, yielded a closed circle when log K-T and log K-R were plotted against log L-0 and log L-4 respectively, showing novel phenomena that L-0 and L-4 have a maximal value and a minimal value, respectively, and K-T and K-R vary by more than three orders of magnitude. These phenomena were successfully described by a global allostery model, which mathematically keeps the frame work of the MWC model, but allows that K-T under a set of solution conditions becomes larger than K-R under another set of solution conditions and postulates that a representative allosteric effector binds to both the T and R states with a lower affinity but with a larger stoichiometry for the R state than for the T state. Thus, this global model can describe any given OEC measured under universal solution conditions with the single adjustable parameter, the concentration of the representative effector. (C) 2002 Elsevier Science B.V. All rights reserved.