Oxygen transfer conductance of human red blood cells at varied pH and temperature

The influence of temperature (varied from 37 to 7 degrees C) and of medium pH (varied from 7.7 to 7.1) on the kinetics of O2 uptake and release by human red blood cells (RBC) under stopped-flow conditions was investigated by double-beam spectrophotometry. From the rate of O2 saturation change and the mean effective PO2 difference between the medium and the Hb of RBC, the specific transfer conductance for O2, G, was calculated. The temperature coefficient, Q10, of G for O2 uptake averaged 1.17, activation energy, Ea, 2.6 kcal/mol O2; the average values for O2 release were: Q10 = 1.32, Ea = 4.8 kcal/mol O2. The G value for release of O2 from oxyhemoglobin solution, Gsol, yielded Q10 = 2.25, Ea = 13.5 kcal/mol O2. Comparison of these Q10 and Ea values with those for diffusion of O2 and hemoglobin in aqueous media leads to the conclusion that in the stopped-flow condition the conductance for O2 transfer was mainly limited by diffusion of O2 and hemoglobin in the red cell interior and by diffusion of O2 in the medium, and to a lesser degree by chemical reaction kinetics. This was further supported by the lack of dependence of O2 transfer conductance values on pH.