The interaction of haemoglobin, magnesium, organic phosphates and band 3 protein in nucleated and anucleated erythrocytes

The anion influx was measured in order to study the interaction among organic phosphates, magnesium, haemoglobin and the N-terminal of the cytoplasmic domain of band 3 protein in human, chicken and trout erythrocytes. The rate constant for SO4 2 influx in human and trout erythrocytes increased significantly when it was measured with an increased concentration of intracellular Mg2þ. The SO4 2 influx was also measured in human erythrocyte ghosts in the presence and absence of Mg2þ. The smaller activation provoked by Mg2þ in ghosts could be caused by the presence of a small quantity of haemoglobin which remained inside. The SO4 2 uptake in chicken erythrocytes in the presence and in absence of Mg2þ was characterized by very similar rate constants. The results suggest that the small increase in intracellular Mg2þ in the erythrocytes involves an increase in the formation of Mg2þ-ATP and Mg2þ-2,3 BPG complexes reducing the affinity of the organic phosphates for Hb. This new situation may influence the functions of the anion transporter with consequent variations of SO4 2 influx throughout the erythrocyte membrane in human and in trout erythrocytes, whereas in chicken RBCs this function cannot occur and, in fact, no increase in sulphate influx was noticeable. The measurement of Hb/O2 affinity by the use of alternating fixed and variable concentrations of organic phosphates and Mg2þ, confirms the interactions between these elements and their effect on the mechanism of the affinity. When we measured the sulphate influx in the presence of DIDS we found some differences in the three types of cells.