MAGNESIUM-BASED TEMPERATURE-DEPENDENCE OF THE ATP CHEMICAL-SHIFT SEPARATION DELTA(ALPHA-BETA) AND ITS RELATION TO INTRACELLULAR FREE MAGNESIUM

Proton-decoupled P-31 NMR spectroscopy was performed in vitro and in v ivo in humans to investigate the temperature dependence of the chemica l-shift separation delta(alpha beta) between the alpha- and beta-phosp horus resonances and the P-31-P-31 coupling constants of ATP using a 1 .5 T whole-body imager. In vitro in the presence of magnesium, a linea r temperature dependence of delta(alpha beta) was found that varied sy stematically with Mg-to-ATP ratio (R), This needs to be considered in studies where delta(alpha beta) is used to determine temperature. A se cond important point is the temperature dependence of -0.0128 +/- 0.00 02 ppm/degrees C (mean +/- SD, n = 6) of the chemical-shift limit delt a(alpha beta)(MgATP)(T) Of mostly mono-magnesium-complexed ATP found a t R = 2.2 +/- 0.2, This parameter is used in combination with the temp erature dependences of the uncomplexed limit delta(alpha beta)(ATP)(T) and the dissociation constant K-D(MgATP)(T) for the determination of [Mg-free(2+)] at different temperatures. Preliminary studies in vivo s how that delta(alpha beta) also decreases in human skeletal muscle wit h increasing temperature, similarly to the in vitro results. Therefore , interpretations of differences in delta(alpha beta) found in vivo mu st consider even small temperature differences to avoid significant er rors in the determination of [Mg-free(2+)]. (C) 1996 Academic Press, I nc.