Covalent immobilization of a halophilic, alkalithermostable lipase LipR2 on Florisil® nanoparticles for production of alkyl levulinates.

ABSTRACT

A novel halophilic, alkalithermostable lipase LipR2 from Alkalispirillum sp. NM-ROO2 was cloned and expressed. LipR2 was covalently immobilized on Florisil® functionalized with glutaraldehyde. Protein binding efficiency of functionalized Florisil® was 94.7%. Immobilized LipR2 retained 97.5% of specific activity of the free enzyme. Free LipR2 has maximal activity at 52 °C, pH 9.3 and 1.9 M NaCl and is resistant to surfactants and organic solvents. Immobilization enhanced LipR2's extreme characteristics, and increased thermostability of LipR2 with the half-life at 50 °C increasing three-fold. Immobilized LipR2 was used as a biocatalyst for esterification of levulinic acid with n-butanol. Under optimal conditions, a 45.9% ester yield was obtained after 12 h. Immobilized LipR2 catalyzed production of ethyl levulinate and 1-dodecyl levulinate with 48.8% and 26.2% ester yields, respectively. When used in repetitive batch esterification, LipR2 retained 69%, 57% and 18.5% of initial activity on esterification of levulinic acid with ethanol, n-butanol and 1-dodecanol, respectively.