Whole-cell conversion of cyclohexanone to ε-caprolactone was attempted by recombinant Escherichia coli BL21(DE3) expressing cyclohexanone monooxygenase (CHMO) of Acinetobacter calcoaceticus NCIMB 9871. High concentrations of cyclohexanone and ε-caprolactone reduced CHMO-mediated bioconversion of cyclohexanone to ε-caprolactone in the resting recombinant E. coli cells. Metabolically active cells were employed by adopting a fed-batch culture to improve the production of ε-caprolactone from cyclohexanone. A glucose-limited fed-batch Baeyer-Villiger oxidation where a cyclohexanone level was maintained less than 6 g/l resulted in a maximum ε-caprolactone concentration of 11.0 g/l. The maximum ε-caprolactone concentration was improved further to 15.3 g/l by coexpression of glucose-6-phosphate dehydrogenase, an NADPH-generating enzyme encoded by the zwf gene which corresponded to a 39% enhancement in ε-caprolactone concentration compared with the control experiment performed under the same conditions.
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Acknowledgments This work was supported by the Korea Energy Management Corporation. W.H. Lee was supported by the Korea Ministry of Education through the BK21 program. M.D. Kim was supported in part by MAF/ARPC through Grape Research Project Group.
- Cyclohexanone monooxygenase
- Escherichia coli
- Glucose 6-phosphate dehydrogenase
- Substrate/product inhibition