Purification and characterization of a highly enantioselective epoxide hydrolase from Aspergillus niger

The epoxide hydrolase from Aspergillus niger was purified to homogeneity us ing a four-step procedure and p-nitrostyrene oxide (pNSO) as substrate. The enzyme was purified 246-fold with 4% activity yield. The protein is a tetr amer composed of four identical subunits of molecular mass 45 kDa. Maximum activity was observed at 40 degrees C, pH 7.0, and with dimethylformamide a s cosolvent to dissolve pNSO. Hydrolysis of pNSO was highly enantioselectiv e, with an E value (i.e. enantiomeric ratio) of 40 and a high regioselectiv ity (97%) for the less hindered carbon atom of the epoxide. This enzyme may be a good biocatalyst for the preparation of enantiopure epoxides or diols .