Effect of the weakly acidic uncoupler 2,4-dinitrophenol and dimethyl sulfoxide on the coordination of Mg2+ with ATP. Possible mechanism of activation of the isolated F1-ATPase by 2,4-dinitrophenol.
The exchange rate constants between Mg2(+)-free and Mg2(+)-bound ATP were determined under various conditions by line shape analysis of the 31P-NMR spectrum based on the exchange reaction, and the thermodynamic parameters of this exchange reaction were determined from the temperature dependence of its rate constants. Analysis of the activation enthalpy change delta H showed that Mg2+ is coordinated with the beta- and gamma-phosphoryl groups of ATP asymmetrically, being in closer proximity to the beta-phosphoryl group. The weakly acidic uncoupler 2,4-dinitrophenol increased this asymmetric coordination of Mg2+, and this effect was enhanced by the further addition of dimethyl sulfoxide. The hydrolysis of ATP in aqueous solution correlated well with the degree of asymmetry of Mg2+ coordination. Thus, this asymmetric coordination specifically weakens the O-P gamma bond at which specific cleavage of ATP catalyzed by most ATPases takes place in the presence of Mg2+. In this paper, the mechanism of activation of isolated ATPase (F1-ATPase) by 2,4-dinitrophenol, and that of ATP synthesis by isolated F1-ATPase in the presence of dimethyl sulfoxide are considered on the basis of these results. The essential role of the OH group of Ser-174 of the beta-subunit of F1-ATPase in ATP hydrolysis is also discussed.