title: Enhancement of the rate of pyrophosphate hydrolysis by nonenzymatic catalysts and by inorganic pyrophosphatase.
abstract: To estimate the proficiency of inorganic pyrophosphatase as a catalyst, (31)P NMR was used to determine rate constants and thermodynamics of activation for the spontaneous hydrolysis of inorganic pyrophosphate (PP(i)) in the presence and absence of Mg(2+) at elevated temperatures. These values were compared with rate constants and activation parameters determined for the reaction catalyzed by Escherichia coli inorganic pyrophosphatase using isothermal titration calorimetry. At 25 °C and pH 8.5, the hydrolysis of MgPP(i)(2-) proceeds with a rate constant of 2.8 × 10(-10) s(-1), whereas E. coli pyrophosphatase was found to have a turnover number of 570 s(-1) under the same conditions. The resulting rate enhancement (2 × 10(12)-fold) is achieved entirely by reducing the enthalpy of activation (ΔΔH(‡) = -16.6 kcal/mol). The presence of Mg(2+) ions or the transfer of the substrate from bulk water to dimethyl sulfoxide was found to increase the rate of pyrophosphate hydrolysis by as much as ∼ 10(6)-fold. Transfer to dimethyl sulfoxide accelerated PP(i) hydrolysis by reducing the enthalpy of activation. Mg(2+) increased the rate of PP(i) hydrolysis by both increasing the entropy of activation and reducing the enthalpy of activation.
authors: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors: Randy B
authors: RB
authors: Stockbridge
authors: Richard
authors: R
authors: Wolfenden
mesh_terms: D002384:Catalysis; D011756:Diphosphates / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D043564:Inorganic Pyrophosphatase / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*
chemical_list: D011756:Diphosphates; D029968:Escherichia coli Proteins; D043564:Inorganic Pyrophosphatase; D008274:Magnesium