Interaction of Haemoglobin with Ions

Abstract

The intracellular distribution of ATP, 2,3‐bisphosphoglycerate( P 2 ‐glycerate) and Mg 2+ was calculated for the oxygenated and deoxygenated human erythrocyte for the normal range and that of pathophysiological variations based on the association constants of the relevant complexes. The data indicate that about 20% of ATP is bound both in the oxygenated and deoxygenated cells, while 39 and 73% of P 2 ‐glycerate is bound under these conditions. An increase of the free Mg 2+ concentration from 0.7 to 1.1 mM is produced by complete deoxygenation of haemoglobin. The calculations would indicate that during deoxygenation of haemoglobin the hexokinase reacts to the increased concentration of the activator Mg 2+ and the decline of the inhibitor P 2 ‐glycerate with an elevation of its activity which corresponds to experimental data on intact erythrocytes. The P 2 ‐glycerate formation rate in deoxygenated cells is stimulated about 2.5 times in comparison to oxygenated cells as estimated from the free concentration of P 2 ‐glycerate and the kinetic constants of bisphosphoglycerate mutase. An assessment of the possible influence of other anions including bicarbonate shows that the distribution of the species of ATP, P 2 ‐glycerate and Mg 2+ are changed by less than 20%. Together with the data presented in the accompanying paper, the results given here indicate that the constants and estimates are approximately valid for intracellular conditions.