Purification and characterisation of a thermostable alkaline lipase from a new thermophilic Bacillus sp. RSJ-1

Abstract

An extracellular alkaline lipase from a new thermophilic Bacillus sp. RSJ-1 was purified to homogeneity by ultrafiltration, followed by ammonium sulfate precipitation, dialysis, Q-Sepharose ion exchange chromatography and Sephacryl S-200 SF gel filtration chromatography. This purification protocol resulted in a 201-fold purification of lipase with 19.7% final yield and the relative molecular weight of the enzyme was determined to be 37 kDa by SDS-PAGE. The kinetic characterisation of the purified enzyme exhibited maximum activity at 50 °C and pH 8.0–9.0. It was stable at 50 °C for 60 min and retained >90% of its original activity for 120 min. The half lives at 55, 60, 65, 70 and 75 °C were 240, 150, 90, 45 and 30 min, respectively. The enzyme was also highly stable in a pH range of 8.0–9.0 for 120 min. The enzyme activity was promoted in the presence of Ca 2+, Na +, Mg 2+ and Ba 2+ and was strongly inhibited by Cs +, K +, Co 2+ and Zn 2+. EDTA did not affect the enzyme activity, whereas the presence of various oxidizing agents, reducing agents and some surfactants, reduced the enzyme activity. The enzyme was highly stable in the presence of some commercial detergent formulations. The values of K m and V max, as calculated from the Lineweaver–Burk plot, were 2.2 mg/ml and 1429 U/ml, respectively.