Two novel lipases purified from rice bran displaying lipolytic and esterification activities

In this study, two novel lipases, rice bran lipase 1 (RBL1) and rice bran lipase 2 (RBL2), were first identified in rice (Oryza sativa) bran. Through the purification by ammonium sulfate precipitation, ion-exchange chromatography and size-exclusion chromatography, RBL1 and RBL2 were purified to 36- and 339-fold with the final specific activity of 4.73 and 44.06 U/mg, respectively. The purified RBL1 and RBL2 had the molecular weight of 18.8 and 35.5 kDa, respectively. The K_m values of RBL1 and RBL2 were 0.766 and 0.432 mM while catalytic efficiency (k_cat/K_m) values of RBL1 and RBL2 were 102.4 and 2559.3 s^-1/mM, respectively. RBL1 and RBL2 both showed esterification activity, but had no transesterification activity. In a solvent-free system, RBL1 and RBL2 exhibited degree of esterification (ED) of 4.4% and 6.5%, respectively. These two novel lipases exerted great properties for their potentials in industrial applications. First, RBL1 and RBL2 showed both mild reaction pH of 7.0 and temperature of 35 °C and 50 °C, respectively. Secondly, they showed great tolerance to several organic solvents and detergents while RBL1 exhibited great pH stability across a very broad range of pH (pH 3-12). Lastly and most importantly, RBL1 and RBL2 both exhibited esterification activity better than a commercial lipase, Candida rugosa lipase (CRL), in a solvent-free system. In conclusion, two novel lipases, RBL1 and RBL2, are different from published native lipases in rice bran and may be alternative potential candidates of biocatalysts contributing to the development of diverse industrial application fields.