Reaction rates of oxygen with hemoglobin measured by non-equilibrium facilitated oxygen diffusion through hemoglobin solutions

The purpose of this study waste verify the concept of non-equilibrium facil itated oxygen diffusion. This work succeeds our previous study, where facil itated oxygen diffusion by hemoglobin was measured at conditions of chemica l equilibrium, and which yielded diffusion coefficients of hemoglobin and o f oxygen. In the present work chemical non-equilibrium was induced using ve ry thin diffusion layers. As a result, facilitation was decreased as predic ted by theory. Thus, this work presents the first experimental demonstratio n of non-equilibrium facilitated oxygen diffusion. In addition, association and dissociation rate parameters of the reaction between oxygen and bovine and human hemoglobin were calculated and the effect of the homotropic and heterotropic interactions on each rate parameter was demonstrated The resul ts indicate that the homotropic interaction - which leads to increasing oxy gen affinity with increasing oxygenation; is predominantly due to an increa se in the association rate. The heterotropic interaction - which leads to d ecreasing oxygen affinity by anionic ligands - appears to be effected in tw o ways. Cl- increases the dissociation rate. In contrast, 2,3-diphosphoglyc erate decreases the association rate. (C) 2001 Elsevier Science B.V. All ri ghts reserved.