Using the beta/alpha peak-height ratio of ATP in 31P NMR spectra to measure free [Mg2+]: theoretical and practical problems.

A recently described alternative method for determining free [Mg2+] in cells and tissue with 31P NMR spectroscopy, which is based on the peak-height ratio of the beta and alpha resonances of ATP (h(beta/alpha)) [J. Biol. Chem. 271, 21141-21150 (1996)], was found to have numerous problems. These problems include a flaw in the basic multiple equilibrium analysis, the inapplicability of the calibration curve to in vivo studies, and a lack of sensitivity of the measured ratio to changes in free [Mg2+] at 'clinical' field strengths. This suggests that the use of this procedure will be very limited.