The physiological consequences of changes in oxygen affinity in the red cell enzyme defects.

Previous speakers have outlined the genetics and molecular pathology of the defects of enzymes of the glycolytic pathway. Recent work has shown that not only is glycolysis necessary for maintaining the integrity of the red cell and preventing the denaturation of haemoglobin by methaemoglobin formation or oxidation of the sulphydryl groups but it is intimately concerned with the control of oxygen affinity of the red cells. The action is mediated through the glycolytic intermediate 2,3 diphosphoglycerate (2,3-DPG). It has been known for a long time that 2,3-DPG occurs in the red cell in much higher concentration than in other cells, varying between 13-5 and 15-5 ,umol/g Hb (3-8-4-5 mmol/l packed cells). In 1967 two groups of workers showed independently that 2,3-DPG causes a marked lowering oftheoxygen affinity of haemoglobin and changes in the level of 2,3-DPG in the red cell cause a change in the position of the red cell (fig 1) or whole blood oxygen dissociation curve, a rise of 2,3-DPG causing a fall in oxygen affinity. This modulating effect of2,3-DPG on the oxygen affinity will alter the amount of oxygen released by each gram of haemoglobin as it passes