Thermally responsive reversed micelles for immobilization of enzymes

In this study, thermally responsive alkyl end-capped poly(N-isopropylacrylamide-co-acrylic acid) amphiphilic copolymers were synthesized, and successfully utilized to fabricate reversed micelles and immobilize enzymes. Transmission electron microscopy (TEM) study showed that the reversed micelles were spherical in nature. The activity of Candida rugosa lipase immobilized in the reversed micelles towards catalyzing the esterification of lauric acid and 1-propanol was analyzed in comparison with naked enzyme. Immobilized lipase provided much greater catalytic activity. In addition, the effects of pH, water content, polymer and enzyme concentration on the catalytic activity were investigated. The optimized fabrication conditions of lipase-loaded reversed micelles, under which lipase gave the highest activity, were as follows: polymer concentration, 12 mg mL(-1); enzyme concentration, 25 mg mL(-1) phosphate buffered saline (PBS); pH, 7.4; W-0 ([water]/[surfactant]), 83.3. Lipase immobilized in these micelles was much more stable than that in conventional sodium bis(2-ethylhexyl) sulfosuccinate micelles. More importantly, the size of lipase-immobilized micelles decreased, and the enzyme solution precipitated from the reaction mixture when the temperature increased to a value slightly higher than the lower critical solution temperature (LCST) of the polymer. The recovery rate of enzyme was about 75%. The alpha-helix structure of the recovered lipase remained intact. In addition, the enzymatic reaction was terminated after raising the environmental temperature slightly above the LCST. These thermally responsive micelles may make a promising system for enzyme immobilization.