Comparison of hydrolytic activities in aqueous and organic media for lipases immobilized on poly(acrylonitrile-co-maleic acid) ultrafiltration hollow fiber membrane

A novel matrix, poly(acrylonitrile-co-maleic acid) (PANCMA) ultrafiltration hollow fiber membrane, was used for enzyme immobilization. Lipase from Candida rugosa was covalently immobilized onto this membrane surface on which the carboxyl groups were activated with 1-ethyl-3-(dimethyl-aminopropyl) carbodiimide hydrochloride/N-hydroxyl succinimide as coupling agent. Using the hydrolysis reaction of p-nitrophenyl palmitate in aqueous and organic media, the properties of the immobilized lipase were assayed and compared with those of the free ones. Compared to the free enzyme (at 37 °C), it was found that the maximum activity was observed at 45 °C for the immobilized enzyme in the aqueous medium. On the other hand, the amount of added water in the organic medium of heptane showed greater effect on the reaction rate for the free lipase than the immobilized ones. The kinetic constants of the free and immobilized lipases, Km and Vmax, were assayed in the two media. Results indicated that the enzyme activity in heptane increased due to the immobilization and the specific activity was 0.233 U/mg for the immobilized lipase, 0.204 U/mg for the free ones, respectively. The residual activities of the immobilized enzyme were 62% in aqueous media and 67% in organic media, after 10 reuses.