Intracellular Mg2+ regulates ADP phosphorylation and adenine nucleotide synthesis in human erythrocytes.
13C- and 31P-NMR were used in methylene blue-treated human erythrocytes to determine the dependence on intracellular Mg2+ concentration ([Mg2+]i) of the pentose phosphate pathway (PPP), the glycolytic pathway, and adenine nucleotide synthesis. The PPP flux had an [Mg2+]i at half-maximal velocity ([Mg2+]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 [Mg2+]i as flux through phosphofructokinase was increased ([Mg2+]i,0.5 = 0.16 mM). [Mg2+]i,0.5 of phosphoglycerate kinase flux, which equals net ADP phosphorylation rate, was 0.27 mM, well within the physiological [Mg2+]i range. The rate of adenine nucleotide synthesis from [2-13C]glucose-derived ribose 5-phosphate and exogenous adenine also exhibited dependence on [Mg2+]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 [Mg2+]i at physiological ion concentrations, but both ADP phosphorylation and adenine nucleotide synthesis are likely to be regulated by normal fluctuations in [Mg2+]i.
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Department of Surgery, George Washington University Medical Center, Washington, District of Columbia 20037, USA.
Salem
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Laughlin
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D000227:Adenine Nucleotides / Q000096:biosynthesis*; D000244:Adenosine Diphosphate / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D008274:Magnesium / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D010427:Pentose Phosphate Pathway / Q000502:physiology; D010732:Phosphofructokinase-1 / Q000378:metabolism; D010766:Phosphorylation
D000227:Adenine Nucleotides; D019298:Glucose-6-Phosphate; D000244:Adenosine Diphosphate; D010732:Phosphofructokinase-1; D008274:Magnesium; D005947:Glucose