Modulation of the activity and selectivity of the immobilized lipases by surfactants and solvents
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Most of lipases are in equilibrium between a majority inactive closed form and a minority active open form in aqueous media. Perhaps, a certain stabilization of these open forms of lipases could be achieved in the presence of cosolvents or surfactants in the reaction medium. Three commercial lipases were studied (from Thermomyces lanuginosa (TLL), Candida Antarctica fraction B (CALB) and Lecitase (LEC)). Different derivatives were tested: TLL and LEC were adsorbed on an anionic exchanger and their activity strongly depends on the equilibrium between their open and closed form and CALB was adsorbed on a hydrophobic support when the open form was already stabilized by the support. Derivatives ionically adsorbed were hyperactivated by surfactans as well as by cosolvents: the activity of LEC increased 12 times in the presence of 15–20% of ethanol. CALB adsorbed on hydrophobic supports was hardly hyperactivated and even it was inhibited. The modification of the rate of covalent modification of the catalytic Ser seems to confirm that the observed hyperactivations were due to a stabilization of the open form of the adsorbed lipases (TLL and LEC). The hydrolysis of sardine oil was also studied in the presence or absence of surfactants and cosolvents. An interesting improvement in the ability of derivatives to discriminate the release of eicosipentaenic acid (EPA) and docosahexaenicacid (DHA) was found.
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