Constant Enthalpy Change Value during Pyrophosphate Hydrolysis within the Physiological Limits of NaCl

A decrease in water activity was thought to result in smaller enthalpy change values during PPi hydrolysis, indicating the importance of solvation for the reaction. However, the physiological significance of this phenomenon is unknown. Here, we combined biochemistry and calorimetry to solve this pro...

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Bibliographic Details
Published in:The Journal of biological chemistry 2013-10, Vol.288 (41), p.29247-29251
Main Authors: Wakai, Satoshi, Kidokoro, Shun-ichi, Masaki, Kazuo, Nakasone, Kaoru, Sambongi, Yoshihiro
Format: Article
Language:English
Subjects:
Archaeal Proteins - metabolism
Biocatalysis
Bioenergetics
Biophysics
Calorimetry - methods
Diphosphates - chemistry
Diphosphates - metabolism
Enthalpy Change
Enzyme Catalysis
Escherichia coli Proteins - metabolism
Haloarcula - enzymology
Halophile
Hydrolysis - drug effects
Inorganic Pyrophosphatase - metabolism
Isothermal Titration Calorimetry
Molecular Biophysics
NaCl
Pyrophosphate
Saccharomyces cerevisiae Proteins - metabolism
Sodium Chloride - chemistry
Sodium Chloride - pharmacology
Solvents - chemistry
Solvents - pharmacology
Thermodynamics
Water Activity
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Summary:A decrease in water activity was thought to result in smaller enthalpy change values during PPi hydrolysis, indicating the importance of solvation for the reaction. However, the physiological significance of this phenomenon is unknown. Here, we combined biochemistry and calorimetry to solve this problem using NaCl, a physiologically occurring water activity-reducing reagent. The pyrophosphatase activities of extremely halophilic Haloarcula japonica, which can grow at ∼4 m NaCl, and non-halophilic Escherichia coli and Saccharomyces cerevisiae were maximal at 2.0 and 0.1 m NaCl, respectively. Thus, halophilic and non-halophilic pyrophosphatases exhibit distinct maximal activities at different NaCl concentration ranges. Upon calorimetry, the same exothermic enthalpy change of −35 kJ/mol was obtained for the halophile and non-halophiles at 1.5–4.0 and 0.1–2.0 m NaCl, respectively. These results show that solvation changes caused by up to 4.0 m NaCl (water activity of ∼0.84) do not affect the enthalpy change in PPi hydrolysis. It has been postulated that PPi is an ATP analog, having a so-called high energy phosphate bond, and that the hydrolysis of both compounds is enthalpically driven. Therefore, our results indicate that the hydrolysis of high energy phosphate compounds, which are responsible for biological energy conversion, is enthalpically driven within the physiological limits of NaCl. Background: Decreased water activity was thought to result in smaller enthalpy change values during pyrophosphate hydrolysis. Results: The enthalpy change in pyrophosphate hydrolysis caused by halophilic and non-halophilic enzymes is constant up to 4.0 m NaCl. Conclusion: Water activity with high NaCl does not affect the pyrophosphate hydrolysis enthalpy change. Significance: Biological energy conversion is enthalpically driven within the physiological limits of NaCl.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M113.502963