Phosphorus J-coupling constants of ATP in human brain.

Proton decoupled 31P NMR spectroscopy of the occipital brain of healthy volunteers was performed with a 1.5 T whole-body imager. By use of two-dimensional chemical-shift imaging in combination with slice-selective excitation well resolved localized spectra (38 ml) were obtained within 34 min from which the homonuclear 31P-31P J-coupling constants of ATP could be determined: J(gammabeta) = 16.1 Hz +/- 0.2 Hz and J(alphabeta) = 16.3 Hz +/- 0.1 Hz (mean +/- SEM, n = 14). Both, the J-coupling constants and the chemical-shift difference between alpha- and beta-ATP (delta(alphabeta) = 8.61 ppm +/- 0.01 ppm) were used to calculate the concentration of intracellular free magnesium. The concentrations are 0.39 mM +/- 0.09 mM by using the average of both coupling constants of each spectrum, which is in fair agreement with 0.32 mM +/- 0.01 mM obtained from the chemical shift of alpha and beta phosphate resonances, which is the more accurate result.