Purification and biochemical characterization of an extracellular lipase from Pseudomonas fluorescens MTCC 2421

An extracellular lipase produced by Pseudomonas fluorescens MTCC 2421 was purified 184.37-fold with a specific activity of 424.04 LU/mg after anion exchange and gel exclusion chromatography. The enzyme is a homomeric protein with an apparent molecular mass of 65.3 kDa. The lipase exhibited hydrolytic resistance toward triglycerides with longer fatty acyl chain length containing unsaturation as evident from the lower V(max) (0.23 mM/mg/min) of the lipase toward glycerol trioleate (C(18:1n9)) compared with the fatty acid triglycerides having short to medium carbon chain lengths (C(18:0-12:0), V(max) 0.32-0.51 mM/mg/min). This indicates a preferential specificity of the lipase toward cleaving shorter carbon chain length fatty acid triglycerides. The lipase exhibited optimum activity at 40 degrees C and pH 8.0, respectively. A combination of Ca(2+) and sorbitol induced a synergistic effect on the thermostability of lipase with a significantly high residual activity (100%) after 30 min at 40 degrees C, as compared to 90.6% after incubation with Ca(2+) alone. The lipase activity was inhibited by Cu(2+) and Fe(2+) (42 and 48%, respectively) at 10 mM. The enzyme lost 31% of its initial activity by 0.001 mM EDTA and 42% by 0.1 mM EDTA. Significant reduction in lipase activity was apparent by 2-mercaptoethanol and phenylmethanesulfonyl fluoride at diluted concentration (0.001 mM), thereby indicating an important role of sulfhydryl groups in the catalytic mechanism.