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Title: Comparison of Fluorescence, 31P NMR, and 7Li NMR Spectroscopic Methods for Investigating Li+/Mg2+ Competition for Biomolecules
Authors: Amari, Louis 
Layden, Brian 
Rong, Qinfen 
Geraldes, Carlos F. G. C. 
Freitas, Duarte Mota de 
Keywords: lithium; biomolecules; ATP; NMR; fluorescence
Issue Date: 1999
Citation: Analytical Biochemistry. 272:1 (1999) 1-7
Abstract: The biochemical action of lithium in the treatment of manic-depressive illness is still unknown. One hypothesis is that Li+ competes for Mg2+-binding sites in biomolecules. We report here our studies on metal ion competition by three distinct methods: fluorescence, 31P NMR, and 7Li NMR spectroscopy, using ATP as a model ligand. By fluorescence spectroscopy, we used the dye, furaptra, by measuring the increases in Mg2+ levels in an ATP solution as Li+ levels were increased in the solution. This increase in Mg2+ levels was indicated by increases in the fluorescence intensity ratio (335/370) of furaptra. By 31P NMR spectroscopy, this competition was demonstrated by changes in the 31P NMR spectrum of ATP. The Li+/Mg2+ competition was indicated by predictable changes in the separation between the [alpha] and [beta] resonances of the phosphates of ATP. For 7Li NMR spectroscopy, spin-lattice relaxation measurements were used, which provided free Li+ concentrations that could be used for determining the free Mg2+ values in ATP solutions. The values of the free Mg2+ concentrations obtained by all three methods were in good agreement. The fluorescence and 7Li NMR methods, however, proved to be more sensitive to low concentrations of Li+ than the 31P NMR method.
DOI: 10.1006/abio.1999.4169
Rights: openAccess
Appears in Collections:FCTUC Ciências da Vida - Artigos em Revistas Internacionais

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