Enantioselective cascade biocatalysis for deracemization of 2-hydroxy acids using a three-enzyme system

Table 1 Catalytic performance of resting cells of recombinant E. coli expressing the (S)-2-HADH from different microorganisms

Entry	Enzyme source	Specific activity (U/g DCW)^a	Conversion of 2a (%)^b	E
1	P. aeruginosa CCTCC M 2011394	<5	5.1	>200
2	P. aeruginosa strain NUST	107.4	48.9	>200
3	B. xenovorans LB400	90.2	49.0	>200
4	P. fluorescens strain EBC191	<5	5.2	N.D.
5	P. putida ATCC 12633	15.0	23.0	N.D.

N.D. not determined
^aThe enzyme assays were performed at 35 °C, pH 7.5 for 10 min. One unit of enzyme activity was defined as the amount of enzyme catalyzing the oxidation of substrate 1a for producing 1.0 µmol of keto acid in 1.0 min under standard assay conditions. The substrate concentration was 20 mM
^bThe conversion of 2-keto acid was calculated when the reactions were carried out for 2 h

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