Encapsulation of lipase within metal-organic framework (MOF) with enhanced activity intensified under ultrasound

The enzyme under lower-intensity ultrasonic irradiation leads to favorable conformational changes, thereby enhancing its activity. In this study, lipase activity was augmented upto 1.6-folds after ultrasonic treatment at 22 kHz and 11.38 W cm(-2) for 25 min. This highly activated lipase was encapsulated within zeolite imidazolate framework-8 (ZIF-8) as a metal-organic framework (MOF) material via facile one-step biomineralization method by simply mixing aqueous solution of 2-methylimidazole (13.3 mmol) and zinc acetate (1.33 mmol) along with sonicated lipase within 10 min at room temperature (28 +/- 2 degrees C). The prepared lipase-MOF was characterized by using FT-IR, FT-Raman, KRD, BET, confocal scanning laser microscopy, TGA and SEM. Further, the thermal stability of lipase embedded MOF was evaluated in the range of 55-75 degrees C on the basis of half-life which showed 3.2 folds increment as against free lipase. In Michaelis-Menten kinetics studies, sonicated lipase entrapped MOF showed nearly same K-m and V-max values as that of sonicated free lipase. Moreover, the immobilized lipase exhibited up to 54% of residual activity after seven successive cycles of reuse, whereas it retained 90% of residual activity till twenty-five days of storage. Finally, the conformational changes occurred in lipase after sonication treatment and encapsulation within MOF were analyzed by using FT-IR data analysis tools and fluorescent spectroscopy.