Enzymological characterization of a novel d-lactate dehydrogenase from and its application in d-phenyllactic acid synthesis.

A novel lactate dehydrogenase gene, named , was cloned from and heterologously expressed in . The lactate dehydrogenase LDH is NADH-dependent with a molecular weight of approximately 39 kDa. It is active at 40 °C and pH 6.5 and stable in a neutral to alkaline environment below 35 °C. The kinetic constants, including maximal reaction rate ( ), apparent Michaelis-Menten constant ( ), turnover number ( ) and catalytic efficiency ( / ) for phenylpyruvic acid were 1.95 U mg, 2.83 mM, 12.29 s, and 4.34 mM s, respectively. Using whole cells of recombinant /pET28a-, without coexpression of a cofactor regeneration system, 20.5 g l d-phenyllactic acid with above 99% was produced from phenylpyruvic acid in a fed-batch biotransformation process, with a productivity of 49.2 g l d. Moreover, LDH has broad substrate specificity to a range of ketones, keto acids and ketonic esters. Taken together, LDH is a promising biocatalyst for the efficient synthesis of d-phenyllactic acid and other fine chemicals.