Continuous-Flow Microreactor-Enhanced Clean NAD+ Regeneration for Biosynthesis of 7-Oxo-lithocholic Acid
Water-forming NAD(P)H oxidases (NOXs) constitute a clean NAD(P)+ regeneration strategy for NAD(P)+-dependent biotransformations to produce high value-added chemicals because they only consume oxygen and generate water. However, the application of NOXs is still challenging because of limited oxygen transfer in batch reactions. Here, we report an efficient continuous-flow microreactor (CFMR) to improve the oxygen transfer and reaction performance in NAD+-dependent chenodeoxycholic acid oxidation catalyzed by 7α-hydroxysteroid dehydrogenase (7α-HSDH) for the production of 7-oxo-lithocholic acid, a key precursor of ursodeoxycholic acid. The recycling efficiency of NAD+ by NOX from Streptococcus mutans (SmNOX) was significantly improved in this CFMR. Compared with a conventional batch stirred tank reactor, the space–time yield of production of 7-oxo-lithocholic acid was increased by 96-fold. Furthermore, the total turnover number of NAD+ was improved 10-fold, and the enzyme consumption number was decreased 7-fold. Combining the NOX/O2 system with this microreactor technology provides a general platform that enables various NAD(P)+-dependent biotransformations in a green and sustainable manner, which will be helpful in the design of ecofriendly bioprocesses for production of functional chemicals on a large scale.
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