Characterization and catalytic properties of free and silica-bound lipase: a comparative study

In the present study, the commercial lipase from Himedia, Mumbai was immobilized on silica gel matrix in the presence of a cross-linking agent, glutaraldehyde. The silica immobilized lipase exposed to 2% glutaraldehyde showed 94.28% binding efficiency. The activities of the free and immobilized enzymes were investigated in the hydrolysis reaction of p-nitrophenyl palmitate. The activities of the free and the immobilized lipases were measured at different pH values and temperatures, and their thermal stability was also determined. The free and silica immobilized lipase possessed optimum hydrolytic activity at 40°C, pH 8.0 at 10 minutes of reaction time. Among p-nitrophenyl esters of fatty acids of different chain lengths, both free and silica immobilized showed maximum activity towards p-NPP with measured Km of free and immobilized lipase was found at 0.13 and 0.349 mM respectively whereas the Vmax of free and immobilized lipase was 5.08 μmol/min/mL and 10.38 μmol/min/mg respectively. The lipase activity was found to be stimulated only in the presence of Cu(2+) ions whereas other metal ions inhibited activity of the lipase. The silica immobilized lipase was quite stable at 55°C and 60°C. The immobilized lipase was recycled up to 6(th) cycle and it retained 52% of its original activity up to 5(th) cycle.