Differential effects of Mg(ii) and Nα-4-tosyl-l-arginine methyl ester hydrochloride on the recognition and catalysis in ATP hydrolysis

Abstract

The supramolecular interactions of Mg(II) and N_α-4-tosyl-L-arginine methyl ester hydrochloride (TAME) with ATP have been investigated using ¹H and ³¹P NMR spectra. Furthermore, the hydrolysis of ATP catalyzed by Mg(II) and TAME has been studied at 60 °C and pH 7 using ³¹P NMR spectra. In the Mg(II)–ATP–TAME ternary system, the binding interaction of Mg²⁺ with ATP involves not only N1 and N7 in the adenine ring but also β- and γ-phosphate of ATP. The binding forces are mainly electrostatic interaction and cation (Mg²⁺)–π interaction. The guanidinium group and the aromatic ring of TAME interacts with ATP by β and γ phosphate and the adenine ring of ATP. The binding forces are mainly electrostatic interactions and π–π stacking. A significant difference between the binary and the ternary system indicates that TAME is essential to the stablization of the intermediate. Kinetic studies show that the hydrolysis rate constant of ATP is 2.16 × 10⁻² h⁻¹ at pH 7 in the Mg(II)–TAME–ATP ternary system. The Mg(II) ion and TAME can accelerate the ATP hydrolysis process. A possible mechanism has been proposed that the hydrolysis occurs through an addition–elimination, in which the phosphoramidate intermediate was observed at 3.21 ppm in the ³¹P NMR of the ternary system. These results provide further information concerning the effect of the key amino acid residue and metal ions as cofactors of ATPase on ATP synthesis/hydrolysis at the molecular level.