Biochemical analysis of a native and proteolytic fragment of a high-molecular-weight thermostable lipase from a mesophilic Bacillus sp.

An extracellular lipase was isolated from the cell-free broth of Bacillus sp. GK 8. The enzyme was purified to 53-fold with a specific activity of 75.7 U mg(-1) of protein and a yield of 31% activity. The apparent molecular mass of the monomeric protein was 108 kDa as estimated by molecular sieving and 112 kDa by SDS-PAGE. The proteolysis of the native molecule yields a low molecular weight component of 11.5 kDa that still retains the active site. It was stable at the pH range of 7.0-10.0 with optimum pH 8.0. The enzyme was stable at 50degreesC for 1 h with a half life of 2 h, 40 min, and 18 min at 60, 65, and 70degreesC, respectively. With p-nitrophenyl laurate as substrate the enzyme exhibited a K-m and V-max, of 3.63 mM and 0.26 muM/min/ml, respectively. Activity was stimulated by Mg2+ (10 mM), Ba2+ (10 mM), and SDS (0.1 mM), but inhibited by EDTA (10 mM), phenylmethane sulfonyl fluoride (100 mM), diethylphenylcarbonate (10 mM), and eserine (10 mM). It hydrolyzes triolein at all positions. The fatty acid specificity of lipase is broad with little preference for C-4 and C-18:1. Thermostability of the proteolytic fragment at 60degreesC was observed to be 37% of the native protein. The native enzyme was completely stable in ethylene glycol and glycerol (30% v/v each) for 60 min at 65 degreesC. (C) 2002 i;isevier Science (USA).