Purification, identification, characterization and catalytic mechanism of two lipases from rice bran (Oryza sativa)

The efficient utilization of rice bran is severely impeded because of the rapid rancidity caused by rice bran lipase, so the investigation of rice bran lipase characteristic and catalytic mechanism was urgently required. The extracted crude proteins from rice bran were purified to obtain two lipases with 16.31 times of purification fold and 10.64% of purification yield. The molecular masses of these two homologous lipases were 34929.00 Da and 34072.00 Da, respectively. Rice bran lipase showed highest catalytic activity at 40.00 °C, pH 7.50 and held good stability below 50.00 °C and at pH 7.00–7.50. Most metal ions (except Na+ and Co+) and organic solvents had significant inhibition effect (P < 0.05) on the purified lipase activity. Surfactants like Tween 80, Triton 100 and sodium dodecyl sulfonate (SDS) decreased the lipase activities significantly (P < 0.05) to 70.88%, 80.08% and 73.74% respectively and cetyltrimethyl ammonium bromide (CTAB) increased the catalytic activity significantly (P < 0.05) to 109.00%. The Ser-His-Asp residues were speculated to be the catalytic center of purified lipases by using the inhibitors (Phenylmethanesulfonyl fluoride (PMSF), diethylpyrocarbonate (DEPC) and Pepstatin) which aimed at specific amino acids and then verified by molecular docking. Therefore, blocking or destroying the Ser-His-Asp catalytic triad might be new choices to restrain the rancidity of rice bran.