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The authors report the first results on an enzyme-induced reaction within the water core of reverse micelles that have been formed in supercritical CO{sub 2} (scCO{sub 2}). By using a perfluoropolyether ammonium carboxylate (PFPE) surfactant, the authors form reverse micelles in scCO{sub 2} with water cores and the authors show that the oxidation of cholesterol by cholesterol oxidase (ChOx) obeys Michaelis-Menten kinetics. The results of their experiments also show that (1) the optimum ChOx activity occurs when the molar ratio of H{sub 2}O-to-PFPE (R) exceeds {approximately}12, (2) the rate constant describing the conversion of the ChOx-cholesterol complex to product ({kappa}{sub cat,app}) is similar to values reported using reverse micelle systems formed in liquid alkanes, (3) the equilibrium constant that describes the ChOx-cholesterol complex dissociation (K{sub m,app}) is optimal at high R values, (4) the best-case K{sub m,app} is {approximately}2-fold better than the value reported using reverse micelles formed in liquid alkanes, (5) there is little change in the ChOx {kappa}{sub cat,app} and K{sub m,app} as the authors adjust the CO{sub 2} pressure between 100 and 260 bar, and (6) the ChOx was active within the PFPE water pool for at least 5 h; however, after 8 or more hours within the PFPE water pool, ChOx became temporarily inactive.
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