Improved catalytic performance of Bacillus megaterium epoxide hydrolase in a medium containing Tween-80

A new epoxide hydrolase with high enantioselectivity toward (R)-glycidyl phenyl ether (R-GPE) was partially purified from Bacillus megaterium strain ECU1001. The maximum activity of the isolated enzyme was observed at 30 degreesC and pH 6.5 in a buffer system with 5% (v/v) of DMSO as a cosolvent. The enzyme was quite stable at pH 7.5 and retained full activity after incubation at 40 degreesC for 6 h. Interestingly, when the cosolvent DMSO was replaced by an emulsifier (Tween-80, 0.5% w/v) as an alternative additive to help disperse the water-insoluble substrate, the apparent activity of the epoxide hydrolase significantly increased by about 1.8-fold, while the temperature optimum shifted from 30 to 40 degreesC and the half-life of the enzyme at 50 degreesC increased by 2.5 times. The enzymatic hydrolysis of rac-GPE was highly enantioselective, with an E-value (enantiomeric ratio) of 69.3 in the Tween-80 emulsion system, which is obviously higher than that (41.2) observed in the DMSO-containing system.