Partial purification and biochemical characterization of an extremely thermo- and pH-stable esterase with great substrate affinity

An esterase from a thermophilic bacterium, Geobacillus sp. DF20, was partially purified. Final purification factor was found to be 64.5-fold using Q-Sepharose ion exchange column chromatography. Native polyacrylamide gel electrophoresis indicated the presence of a single active esterase. The substrate specificity of this esterase was high for p -nitrophenyl butyrate ( p NPB) substrate. The optimum pH and temperature for the enzyme activity were 7.0 and 50 °C, respectively. The pH and heat stability profiles show that this enzyme is more stable under neutral conditions at 50 °C. Km and Vmax values for this esterase acting on p NPB were 0.12 mM and 54.6 U/mg protein, respectively. Presence of 10% (v/v) acetonitrile in the reaction medium indicated that purified enzyme was strongly inhibited. It was also detected that some metal ions affected enzyme activity at different rates. As a result, it was observed that esterase from Geobacillus sp. DF20 has extreme temperature and pH stabilities. Therefore, the stability and Km value of the enzyme make this study interesting when compared with the literature.