Potential pitfall in the determination of free [Mg²⁺] by³¹P NMR when using the β/α-ATP peak height ratio method

Abstract

Recently, Clarke et al., (Clarke K, Kashiwaya Y, King MT, Gates D, Keon CA, Cross HR, Radda GK, Veech RL. The β/α peak height ratio of ATP. A measure of free [Mg ²⁺_free ] using³¹ P NMR, J. Biol. Chem. 1996;271:21142–21150.) reported a new method to noninvasively determine the concentration of intracellular free magnesium ([Mg ²⁺_free ]) based on the measurement of the peak height ratioh _β/α of the β- and α-ATP signals in³¹P NMR spectra.h _β/α varies with Mg_free ²⁺], however, the study presented here shows thath _β/α also strongly depends on the homogeneity of the static magnetic field. For this reason, we performed at a magnetic field strength of 1.5 T³¹P NMR measurements of solutions that mimic intracellular medium. The magnetic field homogeneity was varied by changing the currents in the shim coils, and the effect onh _β/α is demonstrated with and without proton decoupling. In both cases,h _β/α strongly depends on the magnetic field homogeneity and can therefore lead to a pitfall in the determination of [Mg_free ²⁺].