Kinetic modulation of Trichosporon asahii MSR 54 lipase in presence of organic solvents: Altered fatty acid specificity and reversal of enantio selectivity during hydrolytic reactions

An extracellular Trichosporon asahii MSR 54 lipase was purified to homogeneity by ultrafiltration and hydrophobic interaction chromatography. The enzyme is a 54 kDa monomeric protein with PI 5.2. The lipase is optimally active at pH 9.0 and 40 °C and preferred mid to short chain fatty acids during aqueous hydrolysis of triacylglycerides, methyl esters and p-nitrophenyl fatty acid esters. It also exhibited S enantioselectivity towards hydrolysis of ±phenylethylacetate in aqueous medium. In presence of 50% (v/v) organic solvent of varying log P lipase was stable over a period of 24 h. However in microaqueous environment, the enzyme stability was a direct function of log P value. The catalytic efficiency for the hydrolysis of methyl esters of different fatty acid chain length C8:0, C12:0 and C18:0 was altered by addition of any of the organic solvent. There was 3- to 5-fold enhancement for hydrolysis of methyl caprylate in presence of methanol and DMSO and for methyl stearate in presence of ethyl acetate and hexane. On the other hand the efficiency for methyl laurate decreased markedly on the addition of solvent to aqueous system. Interestingly, the fatty acid chain length specificity in an equimolar mixture was inversely related to log P of the solvent. The solvent effect on enantioselective hydrolysis of ±phenylethylacetate revealed reversal of enantioselectivity from S to R enantiomer in the presence of 50% (v/v) 2-propanol and enzyme lost its enantioselective nature in presence of hexane.