Esterification activity of lipase entrapped in reverse micelles formed in liquefied gas

For AOT-water-liquefied gas systems, we studied formation of reverse micelles, entrapping of lipase into water-pools of the reverse micelles, and esterification activity of the entrapped lipase. The formation of reverse micelles was confirmed with visual observation using a dye soluble in water for liquefied ethane and propane, but was not done for liquefied CO2. Water was solubilized as water-pools in large quantity for the system using liquefied propane and in small quantity for that using liquefied ethane. The entrapping of lipase was confirmed for the system of liquefied propane using lipase labelled with a fluorescence probe. The entrapped lipase exhibited high catalytic activity for esterification of lipophilic substrates, though the activity was a little lower than that in AOT reverse micellar solution formed using hexane as an organic medium. The activity varied with mole ratio of water to AOT, [H2O]/[AOT], and was maximized at a certain value of [H2O]/[AOT]. The value of [H2O]/[AOT] almost agreed with that in a AOT-hexane reverse micellar solution.