title: A theoretical study on the catalytic mechanism of Mus musculus adenosine deaminase.
abstract: The catalytic mechanism of Mus musculus adenosine deaminase (ADA) has been studied by quantum mechanics and two-layered ONIOM calculations. Our calculations show that the previously proposed mechanism, involving His238 as the general base to activate the Zn-bound water, has a high activation barrier of about 28 kcal/mol at the proposed rate-determining nucleophilic addition step, and the corresponding calculated kinetic isotope effects are significantly different from the recent experimental observations. We propose a revised mechanism based on calculations, in which Glu217 serves as the general base to abstract the proton of the Zn-bound water, and the protonated Glu217 then activates the substrate for the subsequent nucleophilic addition. The rate-determining step is the proton transfer from Zn-OH to 6-NH(2) of the tetrahedral intermediate, in which His238 serves as a proton shuttle for the proton transfer. The calculated kinetic isotope effects agree well with the experimental data, and calculated activation energy is also consistent with the experimental reaction rate.
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Xian-Hui
authors.initials: XH
authors.lastname: Wu
authors.forename: Guo-Lin
authors.initials: GL
authors.lastname: Zou
authors.forename: Jun-Min
authors.initials: JM
authors.lastname: Quan
authors.forename: Yun-Dong
authors.initials: YD
authors.lastname: Wu
mesh_terms: D000243:Adenosine Deaminase / Q000737:chemistry*; D000818:Animals; D002384:Catalysis; D004735:Energy Transfer; D018698:Glutamic Acid / Q000737:chemistry; D006639:Histidine / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D007700:Kinetics; D051379:Mice; D008956:Models, Chemical; D008958:Models, Molecular; D011487:Protein Conformation; D011789:Quantum Theory; D015032:Zinc / Q000737:chemistry
chemical_list: D017665:Hydroxyl Radical; D018698:Glutamic Acid; D006639:Histidine; D000243:Adenosine Deaminase; D015032:Zinc