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As a valuable versatile building block, L-phenyllactic acid (L-PLA) has numerous applications in the fields of agriculture, pharmaceuticals, and biodegradable plastics. However, both normally chemically synthesized and naturally occurring PLA are racemic, and the production titer of L-PLA is not satisfactory. To improve L-PLA production and reduce the high cost of NADH, an  in vitro  coenzyme regeneration system of NADH was achieved using the glucose dehydrogenase variant  Ls GDH D255C  and introduced into the L-PLA production process. Here an NADH-dependent L-lactate dehydrogenase-encoding variant gene (L- Lcldh 1 Q88A/I229A ) was expressed in  Pichia pastoris  GS115. The specific activity of L- Lc LDH1 Q88A/I229A  (Pp) was as high as 447.6 U/mg at the optimum temperature and pH of 40°C and 5.0, which was 38.26-fold higher than that of wild-type L- Lc LDH1 (Pp). The catalytic efficiency ( k  cat / K  m ) of L- Lc LDH1 Q88A/I229A  (Pp) was 94.3 mM −1  s −1 , which was 67.4- and 25.5-fold higher than that of L- Lc LDH1(Pp) and L- Lc LDH1 Q88A/I229A  (Ec) expressed in  Escherichia coli , respectively .  Optimum reactions of L-PLA production by dual-enzyme catalysis were at 40°C and pH 5.0 with 10.0 U/ml L- Lc LDH1 Q88A/I229A  (Pp) and 4.0 U/ml  Ls GDH D255C . Using 0.1 mM NAD + , 400 mM (65.66 g/L) phenylpyruvic acid was completely hydrolyzed by fed-batch process within 6 h, affording L-PLA with 90.0% yield and over 99.9%  ee  p . This work would be a promising technical strategy for the preparation of L-PLA at an industrial scale.

Enantioselective Biosynthesis of L-Phenyllactic Acid From Phenylpyruvic Acid In Vitro by L-Lactate Dehydrogenase Coupling With Glucose Dehydrogenase