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Free magnesium‐ion concentration in erythrocytes by 31 P NMR: the effect of metabolite–haemoglobin interactions
Author(s) -
Mulquiney Peter J.,
Kuchel Philip W.
Publication year - 1997
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/(sici)1099-1492(199705)10:3<129::aid-nbm459>3.0.co;2-2
Subject(s) - chemistry , metabolite , intracellular , magnesium , ion , biophysics , analytical chemistry (journal) , biochemistry , chromatography , organic chemistry , biology
The effects that haemoglobin–metabolite interactions have on estimates of free magnesium‐ion concentration in human erythrocytes, determined by 31 P NMR [Gupta, R. K. et al., J. Biol. Chem. 253 , 6172–6176 (1978)], were investigated. If the metabolite–haemoglobin association constants of Berger et al. [ Eur. J. Biochem. 38 , 553–562 (1973)] are used in the analysis then the estimates of intracellular free magnesium‐ion concentration made by Gupta et al. (0.25 and 0.67 mM) become 0.43 and 0.60 mM, for oxygenated and deoxygenated cells, respectively. In oxygenated cells, this difference is primarily due to the lower value of K HbMgATP , given by Berger et al. These newly calculated concentrations are in closer agreement with those of Flatman (0.40 mM for oxygenated cells; 0.62 mM for deoxygenated cells) [Flatman, P. W., J. Physiol. 300 , 19–30 (1980)] obtained with the "zero‐point titration' method. In addition, the assumptions that the chemical shift separations between the α‐ and β‐phosphorus resonances of ATP and MgATP are unchanged on association with Hb were shown to be false. Under normal intracellular conditions this may lead to errors of 5–10%. Much larger errors would be possible in cases where significant amounts of ATP or MgATP are bound to Hb. These outcomes place doubt on measurements of intracellular free Mg 2+ concentration made using 31 P NMR if there is no consideration given to the total concentration of 2,3‐bisphosphoglycerate (BPG), ATP and Hb in the sample; the same principle would apply to other cell‐types. © 1997 John Wiley & Sons, Ltd.