ReviewHuman xanthine oxidase recombinant in E. coli: A whole cell catalyst for preparative drug metabolite synthesis

- E. coli for expression of complex, human enyzmes.
- Optimization of coding sequence and biocatalyst production.
- Preparation of authentic human drug metabolites.
- Whole cell biocatalyst for drug metabolite synthesis.

Human xanthine oxidoreductase (XOR), which is responsible for the final steps of the purine metabolism pathway and involved in oxidative drug metabolism, was successfully expressed in Escherichia coli BL21(DE3) Gold. Recombinant human (rh) XOR yielded higher productivity with the gene sequence optimized for expression in E.coli than with the native gene sequence. Induction of XOR expression with lactose or IPTG resulted in complete loss of activity whereas shake flasks cultures using media rather poor in nutrients resulted in functional XOR expression in the stationary phase. LB medium was used for a 25 L fermentation in fed-batch mode, which led to a 5 fold increase of the enzyme productivity when compared to cultivation in shake flasks. Quinazoline was used as a substrate on the semi-preparative scale using an optimized whole cell biotransformation protocol, yielding 73 mg of the isolated product, 4-quinazolinone, from 104 mg of starting material.