Purification and characterisation of a novel steryl esterase from Melanocarpus albomyces

Abstract

A novel steryl esterase from the ascomycete Melanocarpus albomyces was purified using hydrophobic interaction chromatography and anion exchange chromatography, and the enzyme was biochemically characterised. The enzyme has a tetrameric structure with a molecular weight of 238 kDa. Native gel electrophoresis indicated an isoelectric point of 4.5. The enzyme had broad substrate specificity for different steryl esters, p-nitrophenyl esters and triglycerides with long-chain fatty acids. The pH optimum was dependent on the substrate. The pH optimum of lipase activity was at pH 7, whereas cholesteryl esterase and carboxyl esterase activities had optima at pH 5.5 and 5, respectively. The steryl esterase was more stable at lower pH than at values above pH 7. The enzyme retained over 70% of its activity after 5 h incubation at 50 °C. Activity on p-nitrophenyl butyrate was clearly increased by low detergent concentrations (≤0.1%). M. albomyces steryl esterase is considered to be an interesting tool for the enzymatic modifications of wood pitch due to its broad substrate specificity. Treatment of a model pitch simulating the TMP resin showed that both steryl esters and triglycerides were hydrolysed in the presence of a detergent, whereas only triglycerides were degraded in the absence of detergent.