Purification and characterization of the enantioselective esterase from Kluyveromyces marxianus CBS 1553

An intracellular esterase from the yeast Kluyveromyces marxianus CBS 1553 with interesting enantioselective hydrolytic activity towards racemic esters of 1,2-O-isopropylidene glycerol (IPG) was purified and characterized. Optimal culture conditions for the obtainment of the enantioselective esterase on a 5 l-fermentation scale were investigated. Two esterase activities (EST1 and EST2) in the crude cell extract were identified by native PAGE with specific activity staining and separated from each other by anion-exchange chromatography. EST1 showed higher activity and enantioselectivity than EST2 in the resolution of racemic IPG acetate and was further purified by hydrophobic interaction chromatography and preparative electrophoresis (final specific activity ~= 300 U/mg), showing a main protein band with a molecular mass of 29 kDa. EST1 showed optimal activity between pH 8.0 and 10.0 and was stable in the pH range 7.0-10.0. Moreover, it was rather thermostable and active up to 80°C, and retained most of its activity in the presence of 15% (v/v) of various organic solvents. The enzyme showed similar V max in the hydrolysis of the acetate esters of IPG, whereas the K m value towards (S)-IPG acetate was significantly lower than the one towards the (R)-enantiomer (5.3 and 70 uM, respectively). Finally, comparison of EST1 activity in the presence of different glycerol esters and synthetic substrates with different chain lengths showed a strong preference of this biocatalyst for short-chain substrates.