Adair-based hemoglobin equilibrium with oxygen, carbon dioxide and hydrogen ion activity

Abstract

As has been known for over a century, oxygen binding onto hemoglobin is influenced by the activity of hydrogen ions (H+), as well as the concentration of carbon dioxide (CO2). As is also known, the binding of both CO2 and H+ on terminal valine-1 residues is competitive. One-parametric situations of these hemoglobin equilibria at specific levels of H+, O2 or CO2 are also well described. However, we think interpolating or extrapolating this knowledge into an ‘empirical’ function of three independent variables has not yet been completely satisfactory. We present a model that integrates three orthogonal views of hemoglobin oxygenation, titration, and carbamination at different temperatures. The model is based only on chemical principles, Adair's oxygenation steps and Van't Hoff equation of temperature dependences. Our model fits the measurements of the Haldane coefficient and CO2 hemoglobin saturation. It also fits the oxygen dissociation curve influenced by simultaneous changes in H+, CO2 and O2, which makes it a strong candidate for integration into more complex models of blood acid-base with gas transport, where any combination of mentioned substances can appear.