Thermodynamic and kinetic aspects on water vs. organic solvent as reaction media in the enzyme-catalysed reduction of ketones

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Abstract

The stereoselective reduction of ketones catalysed by alcohol dehydrogenase from Thermoanaerobium brockii was studied in different reaction media, hexane at controlled water activities, hexane with 2.5% water (biphasic) and pure water. The reactions were studied in the temperature range from -1 to 50°C. Increasing the water activity from 0.53 to 0.97 increased the reaction rate 16-fold. The rate was further enhanced in hexane when exceeding the water solubility and in pure water the rates were even higher. This was general for all ketones studied. At controlled water activity the entropy of activation (ΔS(≠)) was the dominating factor. Large negative ΔS(≠) values caused low reaction rates at low a(w). When increasing the carbon chain length of the substrate, for reactions in hexane, the decrease of reaction rate was mainly due to a decrease in ΔS(≠). In the comparison between hexane and pure water, ΔG(≠) values were higher in hexane due to higher ΔH(≠) values. The enantioselectivity (E value) increased from 2.6 at water activity 0.53 to 4.6 at water activity 0.97. Changing media from hexane (2.5%, v/v water) to pure water was not affecting the enantioselectivity or the specificity for different ketones. Copyright (C) 1999.

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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biocatalysis and Enzyme Technology

Keywords

  • Alcohol dehydrogenase, Enantioselectivity, Substrate specificity, Thermoanaerobium brockii, Water activity
Original languageEnglish
Pages (from-to)313-322
Number of pages10
JournalBiochimica et Biophysica Acta - Protein Structure and Molecular Enzymology
Volume1430
Issue number2
Publication statusPublished - 1999 Mar 19
Publication categoryResearch
Peer-reviewedYes