Hemoglobin-facilitated diffusion of oxygen: Interfacial and thickness effects

Abstract

The equations of facilitated diffusion were solved numerically for steady state diffusion of oxygen across membranes of hemoglobin and myoglobin. An interfacial resistance was included in the boundary conditions and the dependence of the solutions on membrane thickness and interfacial conductance was studied. The data of Wittenberg on millipore membranes was fitted adequately if a tortuosity factor for the millipore membranes was taken into account. Comparison of the solutions with Wittenberg's data shows that the interfacial conductances must be large, 10 −8 mole/cm 2-sec-mm Hg or larger. More accurate estimates of interfacial conductance could be obtained from data on thin membranes, 1–5 μ, but such data are not available. It was found that the concentration profiles are not independent of thickness and that the facilitation decreases as the membrane thickness decreases. The latter occurs even for zero interfacial resistance and hence cannot be attributed to a back pressure effect. The effect is present because the dissociation reaction at the low P O 2 boundary increasingly becomes the limiting factor in the establishment of the steady state as L decreases.