Thermochemistry of the biochemical reaction: { pyrophosphate(aq)  +  H2O(l)  =  2 phosphate(aq)}

✍ Scribed by Robert N Goldberg; Yadu B Tewari

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 218 KB
• Volume: 34
• Category: Article
• ISSN: 0021-9614
• DOI: 10.1006/jcht.2002.0931

✦ Synopsis

Calorimetric enthalpies of reaction have been measured for the overall biochemical reaction {pyrophosphate(aq) + H 2 O(l) = 2phosphate(aq)}. The reaction was catalyzed by alkaline phosphatase and, to simplify the thermochemistry, was carried out in the absence of Mg 2+ (aq). Measurements were performed with phosphate buffer (pH = 7.19 and 7.94), PIPES buffer (pH = 7.13), and HEPES buffer (pH = 7.86). The results of these measurements were analyzed by using an equilibrium model. These calculations lead to the standard molar enthalpy change r H o m = -(17.3 ± 0.6) kJ • mol -1 (temperature T = 298.15 K and ionic strength I = 0) for the reference reaction

Values of the apparent equilibrium constant K for the overall biochemical reaction from the literature were also analyzed by using the equilibrium model in order to obtain what is believed to be a reliable value for the equilibrium constant K = 4.7 • 10 -4 for the reference reaction. The values of K and r H o m for the reference reaction have been used together with values from the CODATA tables to calculate standard molar formation properties for the pyrophosphate species.