Quantitation of adenosine-5'-triphosphate used for phosphoinositide metabolism in human erythrocytes

The human erythrocyte actively phosphorylates and dephosphorylates phosphatidylinositol present in the membrane in an apparent "futile cycle." Recent reports have proposed that this phosphorylation/dephosphorylation cycle is a significant consumer of adenosine-5'-triphosphate (ATP) in the erythrocyte. This study details two independent techniques for quantitating the ATP consumed by this phosphoinositide futile cycle. With the first technique a quasi-steady-state labeling of erythrocyte ATP with 32P-phosphate was obtained, and the rate of synthesis of 32P-phosphoinositides was then monitored. The second technique used a novel labeling strategy that allowed only ATP to be labeled with 32P; the transfer of 32P from ATP to phosphoinositides was then an independent measure of the ATP consumed for phosphoinositide synthesis. These two techniques documented that 0.5% to 1.0% of net ATP produced by the erythrocyte is used for phosphoinositide synthesis.