Determination of interdependent ligand effects on human red cell oxygen affinity

Abstract

Human whole blood oxygen affinity was determined as P50, i.e. PO2 for oxygen saturation (SO2) = 0.5, in a new system which allows the measurement of SO2, PO2 and pH continuously and independently, with control of PCO2 and temperature. The influence of pH on P50 expressed as the H+ factor (delta log P50/delta pH)PCO2 was measured under conditions of varying PCO2, temperature and concentration of 2,3-diphosphoglycerate (2,3-DPG), resulting in a set of data expressing second-order inter-ligand interactions. The H+ factor appeared to be only slightly dependent on PCO2. Similarly, the CO2 factor (delta log P50/delta log PCO2)pH shows only a minor dependence on pH. The H+ factor in linearly related to the temperature: at 17 degrees C and 42 degrees C the H+ factor is about -0.53 and -0.36, respectively. Likewise, the temperature factor (delta log P50/delta T)PCO2,pH is linearly related to pH. A pilot study on the effect of varying intra-erythrocytic 2,3-DPG concentrations on the oxygen affinity showed that a very low 2,3-DPH/Hb4 ratio apparently does not influence the H+ factor. A high ratio, however, seems to lower the H+ factor considerably.