Intracellular Mg21 regulates ADP phosphorylation and adenine nucleotide synthesis in human erythrocytes

Page, Sarah, Michael Salem, and Maren R. Laughlin. Intracellular Mg21 regulates ADP phosphorylation and adenine nucleotide synthesis in human erythrocytes. Am. J. Physiol. 274 (Endocrinol. Metab. 37): E920–E927, 1998.— 13Cand 31P-NMR were used in methylene blue-treated human erythrocytes to determine the dependence on intracellular Mg21 concentration ([Mg]i) of the pentose phosphate pathway (PPP), the glycolytic pathway, and adenine nucleotide synthesis. The PPP flux had an [Mg]i at half-maximal velocity ([Mg]i,0.5) of 0.02 mM, well below the physiological range (0.2–0.7 mM). Flux through the PPP was reduced at higher [Mg]i as flux through phosphofructokinase was increased ([Mg]i,0.5 5 0.16 mM). [Mg]i,0.5 of phosphoglycerate kinase flux, which equals net ADP phosphorylation rate, was 0.27 mM, well within the physiological [Mg]i range. The rate of adenine nucleotide synthesis from [2-13C]glucosederived ribose 5-phosphate and exogenous adenine also exhibited dependence on [Mg]i but was not saturable up to 1.6 mM. Therefore, net flux through the PPP and glycolytic pathways in erythrocytes is not strongly dependent on [Mg]i at physiological ion concentrations, but both ADP phosphorylation and adenine nucleotide synthesis are likely to be regulated by normal fluctuations in [Mg]i.