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  • Title: Measurement of the dissociation constant of MgATP at physiological nucleotide levels by a combination of 31P NMR and optical absorbance spectroscopy.
    Author: Gupta RK, Gupta P, Yushok WD, Rose ZB.
    Journal: Biochem Biophys Res Commun; 1983 Nov 30; 117(1):210-6. PubMed ID: 6607050.
    Abstract:
    To resolve a controversy in the literature concerning the affinity of Mg++ for ATP to be used in our noninvasive 31P NMR procedure for the determination of free Mg++ in living cells, we have reinvestigated the apparent dissociation constant of MgATP under physiologic ionic conditions and over the cellular range of ATP concentrations by a combination of NMR and optical absorbance techniques. The new combination method utilizes 31P NMR chemical shifts to determine the degree of Mg++ chelation of ATP in a solution containing free ATP and MgATP, and uses a properly calibrated indicator dye, antipyrylazo III, for optical measurement of free Mg++ in the same solution. The data yield an average value of 50 +/- 10 microM for the apparent dissociation constant of MgATP which indicates low levels of free Mg++ (less than 1 mM) in several different types of tissues, including perfused heart muscle, contrary to a recent report in the literature.
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