Hemoglobin oxygen carbon monoxide equilibria with the MWC model

Fractional saturation equations for the Monod, Wyman and Changeux model are derived for the case of two distinct ligands bonding to a host molecule with four ligand sites and two conformational states. A variety of useful graphical studies can be derived from these equations when applied to normal human hemoglobin with O-2 and CO as ligands. For example, the oxygen transport capability of hemoglobin can be assessed at different environmental CO levels and the concentrations of various liganded species can be displayed as a function of fractional saturation with oxygen. In addition, the CO pressure in the tissue, p(CO)(tissue), can be calculated as a function of the tissue oxygen pressure, p(O2)(tissue), at different environmental levels of CO. In an environment of a given CO concentration, p(CO)(tissue) decreases with p(O2)(tissue) until a minimum is reached. Further decrease in p(O2)(tissue) results in a fairly steep rise in p(CO)(tissue). (C) 1998 Elsevier Science B.V. All rights reserved.