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  • Title: A water molecule in the stereospecificity pocket of Candida antarctica lipase B enhances enantioselectivity towards pentan-2-ol.
    Author: Léonard V, Fransson L, Lamare S, Hult K, Graber M.
    Journal: Chembiochem; 2007 Apr 16; 8(6):662-7. PubMed ID: 17328021.
    Abstract:
    The effect of water activity on enzyme-catalyzed enantioselective transesterification was studied by using a solid/gas reactor. The experimental results were compared with predictions from molecular modelling. The system studied was the esterification of pentan-2-ol with methylpropanoate as acyl donor and lipase B from Candida antarctica as catalyst. The data showed a pronounced water-activity effect on both reaction rate and enantioselectivity. The enantioselectivity increased from 100, at water activity close to zero, to a maximum of 320, at a water activity of 0.2. Molecular modelling revealed how a water molecule could bind in the active site and obstruct the binding of the slowly reacting enantiomer. Measurements of enantioselectivity at different water-activity values and temperatures showed that the water molecule had a high affinity for the stereospecificity pocket of the active site with a binding energy of 9 kJ mol-1, and that it lost all its degrees of rotation, corresponding to an entropic energy of 37 J mol-1 K-1.
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