Comparison of fluorescence, (31)P NMR, and (7)Li NMR spectroscopic methods for investigating Li(+)/Mg(2+) competition for biomolecules.
The biochemical action of lithium in the treatment of manic-depressive illness is still unknown. One hypothesis is that Li(+) competes for Mg(2+)-binding sites in biomolecules. We report here our studies on metal ion competition by three distinct methods: fluorescence, (31)P NMR, and (7)Li NMR spectroscopy, using ATP as a model ligand. By fluorescence spectroscopy, we used the dye, furaptra, by measuring the increases in Mg(2+) levels in an ATP solution as Li(+) levels were increased in the solution. This increase in Mg(2+) levels was indicated by increases in the fluorescence intensity ratio (335/370) of furaptra. By (31)P NMR spectroscopy, this competition was demonstrated by changes in the (31)P NMR spectrum of ATP. The Li(+)/Mg(2+) competition was indicated by predictable changes in the separation between the alpha and beta resonances of the phosphates of ATP. For (7)Li NMR spectroscopy, spin-lattice relaxation measurements were used, which provided free Li(+) concentrations that could be used for determining the free Mg(2+) values in ATP solutions. The values of the free Mg(2+) concentrations obtained by all three methods were in good agreement. The fluorescence and (7)Li NMR methods, however, proved to be more sensitive to low concentrations of Li(+) than the (31)P NMR method.
Department of Chemistry, Loyola University Chicago, 6525 North Sheridan Road, Chicago, Illinois 60626, USA.
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Amari
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Layden
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Geraldes
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D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D001714:Bipolar Disorder / Q000188:drug therapy / Q000378:metabolism; D006801:Humans; D008094:Lithium / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010710:Phosphates / Q000378:metabolism; D010758:Phosphorus; D013050:Spectrometry, Fluorescence / Q000379:methods*
D010710:Phosphates; D010758:Phosphorus; D000255:Adenosine Triphosphate; D008094:Lithium; D008274:Magnesium