title: 31P NMR and isothermal titration calorimetry studies on polyoxomolybdates-catalyzed hydrolysis of ATP.
abstract: ATP hydrolysis in the presence of polyoxomolybdates at pH levels of 6, 4, and 2 has been investigated with a help of high pressure liquid chromatography (HPLC) analyses, 31P- and 1H NMR measurements, and isothermal titration calorimetry (ITC). The polyoxomolybdates-induced ATP-hydrolysis proceeded satisfactorily in pH < 6 media at 20 degrees C with an optimum pH level of 4, while it was significantly depressed at low temperature of < or = 5 degrees C. At pH levels of 6 and 4, ADP was a main product, and the involvement of [(PO4)2Mo5O15](6-)-like ATP-molybdate complex as an intermediate was implied. At pH 2 ATP was decomposed to AMP with small generation of ADP through the formation of the ATP-molybdate complex isostructural with [(O3POPO3)Mo6O18(H2O)4]4- as an intermediate. The ITC result at pH 4 showed an occurrence of two types of the exothermic binding reactions between molybdate and ATP with binding constants (K) of 6.61x10(4) and 9.40x10(3) M(-1) and molar enthalpy values (deltaH) of -6.32x10(4) and -4.73x10(3) J mol(-1), respectively. Together with the results of 1H NMR measurements, it is deduced that the molybdates interact with not only phosphate sites in the ATP side-chain, but also adenine-ring with an accompanying aggregation of molybdates at pH 4.
authors.affiliation: Chemical Resources Laboratory, Tokyo Institute of Technology, R1-21, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Ishikawa
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Yamase
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry*; D002151:Calorimetry; D002384:Catalysis; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008982:Molybdenum / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: C044659:molybdate; D008982:Molybdenum; D000255:Adenosine Triphosphate