Interactions of Na+ with haemoglobin-organic phosphate complexes.

Longitudinal and transverse relaxation times were measured in aqueous solutions containing haemoglobin and 2,3-bisphosphoglycerate and in dilute lysates of human erythrocytes. Analysis of the data in terms of calculated excess relaxation rates shows that Na+ interacts with the protein-organic phosphate complex. The comparable magnitude of the effect in the model system and in dilute lysate suggests that intracellular Na+ binds to the haemoglobin-bisphosphate complex. Results obtained with adenosine triphosphate and D-glucose indicate that there is also interaction between Na+ and haemoglobin complexes of these molecules.