Thermodynamic parameters for the interaction of adenosine 5′-diphosphate, and adenosine 5′-triphosphate with Mg²⁺ from 323.15 to 398.15 K

Abstract

The interaction of adenosine 5′-diphosphate (ADP) and adenosine 5′-triphosphate (ATP) with Mg²⁺ in water has been studied calorimetrically at 323.15, 348.15, 373.15, and 398.15 K for ATP and at 348.15 and 373.15 K for ADP. The enthalpies of reaction of Mg²⁺ with ADP and ATP were obtained from the heats of mixing of aqueous solutions of tetramethylammonium salts of ADP and ATP with MgCl₂ solutions in an isothermal flow calorimeter. Equilibrium constant (K), enthalpy change (ΔH°), entropy change (ΔS°), and heat capacity change (ΔCp°) values were calculated for the interaction: Mg²⁺+Lⁿ⁻=MgL²⁻ⁿ and Mg²⁺+MgL²⁻ⁿ=Mg₂L⁴⁻ⁿ, where n=4 for L=ATP and n=3 for L=ADP. The results are consistent with those at lower temperatures. For the two nucleotides studied, the above two reactions are endothermic and entropy-driven in the temperature range studied. Large ΔCp° values for the interaction of Mg²⁺ with ADP with ATP indicate the involvement of phosphate groups of nucleotides in the coordination of Mg²⁺. The coordination of the first and second Mg²⁺ ions involves the phosphate chain in both ADP and ATP. No evidence was found for the involvement of the adenine ring or the ribose moiety in the coordination of Mg²⁺ with these nucleotides. Approximate values of logK, ΔH°, and ΔS°, and ΔCp° for the self-association of ADP and ATP in the presence of Mg²⁺ are also given.