Interaction of ATP with erythroblast glucose-6-phosphate dehydrogenase

ATP, complexed with magnesium and as free anion, binds to rabbit erythroblasts glucose-6-phosphate dehydrogenase (G6PD) inducing significant structural transitions in the enzyme, revealed by a different heat stability. ATP4- facilitates the process of thermal inactivation by inducing the presence of thermolable forms. On the contrary, ATP-Mg protects the enzyme from thermal inactivation. The protection is significant but less marked than that shown by NADP. Kinetic studies indicate a different type of binding between ATP-Mg and ATP4-. Uncomplexed ATP is a competitive inhibitor vs NADP or G6P and it shows a positive cooperative effect. ATP-Mg is an uncompetitive inhibitor vs G6P and competitive vs NADP and it shows a negative cooperativity. A similar behaviour is also shown by complexed and free CTP and GTP.