Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

From 31P NMR measurements made in vitro at 38 degrees C, I = 0.25, pH 5. 75-8.5, and calculated free [Mg2+] from 0 to 5 mM, we show that, within the physiological range of cytosolic free [Mg2+] from 0.25 to 1.5 mM, the chemical shift difference between the alpha- and beta-ATP resonances, deltaalphabeta, changes by only 0.6 ppm. Consequently, we developed new formalisms from known acid and Mg2+ dissociation constants by which the observed chemical shift of Pi, deltaPi, and the peak height ratio of the beta- and alpha-ATP resonances, hbeta/alpha, could be related to free [Mg2+] by simultaneous solution of: [equation: see text] We found that hbeta/alpha changed 2.5-fold as free [Mg2+] varied from 0.25 to 1.5 mM, providing a more sensitive and accurate measure of free cytosolic [Mg2+]. In working rat heart perfused with glucose, free [Mg2+] was 1.0 +/- 0.1 from hbeta/alpha and 1.2 +/- 0.03 from measured [citrate]/[isocitrate] but 0.51 +/- 0.1 from deltaalphabeta. Addition of ketone bodies to the perfusate decreased free [Mg2+] estimated from hbeta/alpha to 0.61 +/- 0.02 and 0.74 +/- 0.11 by [citrate]/[isocitrate] but the estimate from deltaalphabeta was unchanged at 0.46 +/- 0.04 mM. Such differences in estimated free [Mg2+] alter the apparent Keq of the creatine kinase reaction and hence the estimated cytosolic free [SigmaADP].

Original publication




Journal article


J Biol Chem

Publication Date





21142 - 21150


Adenosine Triphosphate, Animals, Citrates, Cytosol, Isocitrates, Magnesium, Magnetic Resonance Spectroscopy, Myocardium, Phosphorus Isotopes, Rats