Catalyzes the NADP dependent reversible and stereospecific interconversion between 2-ketocarboxylic acids and L-2-hydroxy-carboxylic acids. 2-ketoacids with medium chain length (five to six C-atoms) are the best substrates. Homotetramer. Can be applied in an industrial process for the production of L-amino acid. Belongs to the LDH/MDH superfamily. LDH family.