Velocity of oxygen uptake by partly saturated adult and fetal human red cells.

The rate of oxygen uptake by human adult and fetal red cells at 37 degrees C was measured at saturations from zero up to 75% using a double-beam stopped-flow apparatus. Results were expressed in two ways: as k'c, the velocity constant for O2 uptake by the cells, and as theta standard, the number of ml of O2 (STPD) which would be taken up in 1 minute per torr of PO2 difference between the outside and inside of the red cells, by blood with an O2 capacity of 20 vol%. At zero saturation, k'c for adult cells was 99 and for fetal cell was 89 millimolar-1-sec-1. At low saturations there was little changes in adult or fetal k'c but at higher saturations k'c rose and at 75% saturation was 3-4 times its value at zero saturation. In fetal cells, k'c was about 10% less than for adult cells. This difference was statistically significant at low saturations but at higher saturations there was much scatter in the results and the difference between adult and fetal cells was not significant. As saturation rose theta showed little or no change up to 75% saturation. Theoretical analysis of the factors affecting k'c suggested that its rise with increasing SO2 was due to a lowering of the concentration of intracellular deoxyhemoglobin rather than to any increase in reaction rate of oxygen with the hemoglobin molecule.