Magnesium-Based Temperature Dependence of the ATP Chemical-Shift Separation δαβand Its Relation to Intracellular Free Magnesium

Proton-decoupled³¹P NMR spectroscopy was performedin vitroandin vivoin humans to investigate the temperature dependence of the chemical-shift separation δ_αβbetween the α- and β-phosphorus resonances and the³¹P–³¹P coupling constants of ATP using a 1.5 T whole-body imager.In vitroin the presence of magnesium, a linear temperature dependence of δ_αβwas found that varied systematically with Mg-to-ATP ratio (R). This needs to be considered in studies where δ_αβis used to determine temperature. A second important point is the temperature dependence of −0.0128 ± 0.0002 ppm/°C (mean ± SD,n= 6) of the chemical-shift limit δ^MgATP_αβ(T) of mostly mono-magnesium-complexed ATP found atR= 2.2 ± 0.2. This parameter is used in combination with the temperature dependences of the uncomplexed limit δ^ATP_αβ(T) and the dissociation constantK^MgATP_D(T) for the determination of [Mg²⁺_free] at different temperatures. Preliminary studiesin vivoshow that δ_αβalso decreases in human skeletal muscle with increasing temperature, similarly to thein vitroresults. Therefore, interpretations of differences in δ_αβfoundin vivomust consider even small temperature differences to avoid significant errors in the determination of [Mg²⁺_free].