title: Elucidating the Molecular Origin of Hydrolysis Energy of Pyrophosphate in Water.
abstract: The molecular origin of the energy produced by the ATP hydrolysis has been one of the long-standing fundamental issues. A classical view is that the negative hydrolysis free energy of ATP originates from intramolecular effects connected with the backbone P-O bond, so called "high-energy bond". On the other hand, it has also been recognized that solvation effects are essential in determining the hydrolysis free energy. Here, using the 3D-RISM-SCF (three-dimensional reference interaction site model self-consistent field) theory that integrates the ab initio quantum chemistry method and the statistical mechanical theory of liquids, we investigate the molecular origin of hydrolysis free energy of pyrophosphate, an ATP analogue, in water. We demonstrate that our theory quantitatively reproduces the experimental results without the use of empirical parameters. We clarify the crucial role of water in converting the hydrolysis free energy in the gas phase determined solely by intramolecular effects, which ranges from endothermic, thermoneutral, to highly exothermic depending on the charged state of pyrophosphate, into moderately exothermic in the aqueous phase irrespective of the charged state as observed in experimental data. We elucidate that this is brought about by different natures of solute-water interactions depending on the charged state of solute species: the hydration free energy of low-charged state is mainly subjected to short-range hydrogen-bonds, while that of high-charged state is dominated by long-range electrostatic interactions. We thus provide unambiguous evidence on the critical role of water in determining the ATP hydrolysis free energy.
authors.affiliation: Department of Chemistry, Sookmyung Women's University , Cheongpa-ro 47-gil 100, Yongsan-Ku, Seoul 140-742, Korea.
authors.forename: Jooyeon
authors.initials: J
authors.lastname: Hong
authors.affiliation: Department of Chemistry, Faculty of Sciences, Kyusyu University , Fukuoka 812-8581, Japan.
authors.forename: Norio
authors.initials: N
authors.lastname: Yoshida
authors.affiliation: Department of Chemistry, Sookmyung Women's University , Cheongpa-ro 47-gil 100, Yongsan-Ku, Seoul 140-742, Korea.
authors.forename: Song-Ho
authors.initials: SH
authors.lastname: Chong
authors.affiliation: Department of Chemistry, Sookmyung Women's University , Cheongpa-ro 47-gil 100, Yongsan-Ku, Seoul 140-742, Korea.
authors.forename: Chewook
authors.initials: C
authors.lastname: Lee
authors.affiliation: Department of Chemistry, Sookmyung Women's University , Cheongpa-ro 47-gil 100, Yongsan-Ku, Seoul 140-742, Korea.
authors.forename: Sihyun
authors.initials: S
authors.lastname: Ham
authors.affiliation: Department of Theoretical Molecular Science, Institute for Molecular Science , Okazaki 444-8585, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Hirata