Activation of AMP deaminase in human erythrocytes by calcium ions

We examined 5'-AMP aminohydrolase (AMP deaminase, EC 3.5.4.6. AMPD) together with metabolite changes in intact red blood cells from normal human adults under different incubation conditions. Moderate changes occurred in erythrocyte adenylates upon incubation for 1 h at 37 degrees C in the absence of glucose and the concentration of IMP was negligible. Calcium in the incubation medium, at concentrations up to 1.50 mmol l-1 did not influence the nucleotide pattern. Inclusion of the ionophore A 23187 in the incubation medium resulted in a sharp decrease of ATP content at 60 min and increases in AMP and ADP concentrations. A maximally low level of ATP was observed at 60 min of incubation in the presence of both the ionophore and 0.25 mmol l-1 of external calcium. With increasing concentrations of calcium up to 1.50 mmol l-1 in the presence of the ionophore, a significant rise occurred in both IMP and ATP concentrations, whether glucose was present or not, and significant correlations existed between the concentrations of calcium and IMP. The presence of the ionophore together with glucose but without extra calcium in the incubation medium produced the highest concentrations of lactate, indicative of an enhanced glycolytic flux under these conditions. The stimulatory effect of intracellular calcium ions on AMPD activity is discussed.