The regulatory role for magnesium in glycolytic flux of the human erythrocyte

Abstract

31P NMR was used to measure the intracellular free magnesium concentration ([Mg2+](i)) in human erythrocytes while [Mg2+](i) was changed between 0.01 and 1.2 mM using the divalent cationophore A23187. 13C NMR and [2-13C]glucose were used to determine the kinetic effects of [Mg2+](i) by measuring the flux through several parts of the glucose pathway. Glucose utilization was strongly dependent on [Mg2+](i), with half-maximal flux occurring at 0.03 mM. The rate-limiting step was most likely at phosphofructokinase, which has a K(m(Mg2+)) of 0.025 mM in the purified enzyme. Phosphorylated glycolytic intermediate concentration was also strongly dependent on [Mg2+](i) and [MgATP], and glucose transport plus hexokinase may have been partially rate-determining at [Mg2+](i) below 0.1 mM. The pentose phosphate shunt activity was too low to determine the dependence on [Mg2+](i). Phosphoglycerate kinase and 2,3- diphosphoglycerate mutase fluxes were also measured, but were not rate- limiting for glycolysis and showed no Mg2+ dependence. Human erythrocyte [Mg2+](i) varies between 0.2 mM (oxygenated) and 0.6 mM (deoxygenated), well above the measured [Mg2+](i( 1/4 )). It is unlikely, then, that [Mg2+](i) plays a regulatory role in normal erythrocyte glycolysis.