[Mg spin determines adenosinetriphosphate energetics]

The molecular dynamics method DFT:B3LYP (6-31G** basis set, T = 310 K) was used to study interactions between adenosinetriphosphate (ATP), ATP subsystem, and magnesium cofactor [Mg(H2O)6]2+, Mg subsystem, in water environment modeled with 78 water molecules in singlet (S) and triplet (T) states. The lowest in energy singlet (S) and triplet (T) potential energy surfaces, PESs, are remarkably separated in space and direct the Mg cofactor towards the gamma-beta-phosphate oxygens (O1-O2), S path, or towards the beta-alpha-phosphate oxygens (O2-O3), T path. Chelation of the gamma-beta-phosphates and beta2-alpha-phosphates ends, respectively, in the formation of stable, low-energy, ([Mg(H2O)4-(O1-O2)ATP]2-) and metastable, high-energy, ([Mg(H2O)2-(O2-O3)ATP]2-) chelates, differing in the number of water molecules around the Mg. Intersection between the two T PESs produces an unstable state, a result of spin redistribution between the Mg and ATP subsystems. This state, which is sensitive to a hyperfine interaction with the Mg nuclear spin, 25Mg, reveals an unpaired electron spin and initiates the ATP cleavage along the ion-radical path, yielding a highly reactive adenosinemonophosphate ion-radical, *AMP-, earlier observed in the CIDNP (Chemically Induced Dynamic Nuclear Polarization) experiment (A.A. Tulub, 2006). Biological consequences of the findings are discussed.