Abstract
The enthalpy of hydrolysis of the enzyme-catalyzed (heavy meromyosin) conversion of adenosine 5'-triphosphate (ATP) to adenosine 5'-diphosphate (ADP) and inorganic phosphate has been investigated using heat-conduction microcalorimetry. Enthalpies of reaction were measured as a function of ionic strength (0.05-0.66 mol kg-1), pH (6.4-8.8), and temperature (25-37 degrees C) in Tris/HCl buffer. The measured enthalpies were adjusted for the effects of proton ionization and metal ion binding, protonation and interaction with the Tris buffer, and ionic strength effects to obtain a value of delta H0 = -20.5 +/- 0.4 kJ mol-1 at 25 degrees C for the process, ATP4-(aq) + H2O(l) = ADP3-(aq) + HPO2-4(aq) + H+(aq) where aq is aqueous and l is liquid. Heat measurements carried out at different temperatures lead to a value of delta C0p = -237 +/- 30 J mol-1 K-1 for the above process.
Highlights
We note the recent calorimetric measurements on the intermediate stepsof adenosine 5’-triphosphate (ATP) hydrolysis [13,14,15]. .These studies which seeakknowledge of the thermodynamics of the intermediatesteps require, as base-line data, the magnitude of the thermodynamic changes for the overall hydrolysis process
The Tris, HCI, and CaCI2 wereobtained from Fisher Scienthermodynamics of thehydrolysis of ATP was recognized tific
Alberty [2,3,4] a n d by Phillips et al [5]. These reviews empha- 4 ppm; inorganic phosphate < 0.03%;chloride < 0.04%;and moisture sized the need for accurate thermodynamic data for the following reference reaction, by Karl Fischer 8.8%.Chromatographic analysis (Synchropak AX100 weak anion exchange column with a 0.2 M ammonium phosphate mobile phase at pH 2.7) of the ATP sample indicated no impurities
Summary
Vol 261, No 27, Issue of September 25. pp. 12733-12737, 1986 Printed in U.S.A. Thermodynamics of the Hydrolysisof Adenosine 5”triphosphate to Adenosine 5’-diphosphate*. The primary goal is to obtain reliable values for the standard state enthalpy and heat capacity changesfor Process A, the reference reaction for the hydrolysis of ATP Combination of this data with the Gibbs energy change yieldsa value for the entropy changeand a more complete understanding of the thermodynamics of this reaction. The concentrations of the ADP, Tris/HCl, CaCI,, and meromyosinwere essentially identical to those usedin the were carried out at high ionic strengths, probably since the corresponding reaction heat measurements where the reactant ATP enzyme used (myosin) is soluble only under these conditions.
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