A study on the exchange rate of magnesium with ATP.

The exchange process of Mg2+ with ATP was found to be, in many cases, dominated by Mg2+ exchange between ATP and ATP-Mg (a bimolecular reaction) rather than the Mg2+ off-process from ATP-Mg to solution (a unimolecular reaction). The Mg2+ off-rate from ATP-Mg and the rate constant of the bimolecular reaction were determined at 10 and 25 degrees C at pH 7.3, using 31P-NMR at 145.7 MHz. At this resonance frequency intermediate to slow exchange phenomena with respect to the NMR time scale of 2.5 . 10(3) s-1 were observed in ATP resonances. Various implications of these results to studies of biological systems have been pointed out.