Catalyzes the interconversion between the D- and L-isomers of lactate (PubMed:24710389, PubMed:26138974). May act as a rescue enzyme to ensure D-lactate production in physiological conditions where its production by the D-lactate dehydrogenase LdhD is not sufficient (PubMed:16166538). D-Lactate is absolutely required for growth of L.plantarum and is an essential component of the cell wall peptidoglycan in this species, where it is incorporated as the last residue of the muramoyl-pentadepsipeptide peptidoglycan precursor; its incorporation confers high level of vancomycin resistance (PubMed:16166538). (S)-lactate = (R)-lactate Was originally shown to use Ni(2+) as a cofactor (PubMed:24710389), but in fact, the cofactor is a (SCS)Ni pincer complex, a nicotinic acid mononucleotide derivative that is covalently attached to Lys-184 and forms a tridentate pincer complex that coordinates nickel through one metal-carbon and two metal-sulfur bonds (PubMed:26138974, PubMed:27114550). Activation of the apo-enzyme requires the three accessory proteins LarB, LarE and LarC, that are involved in the biosynthesis of the nickel-pincer cofactor of LarA (PubMed:24710389, PubMed:27114550). Inhibited by sulfite that behaves as a mixed inhibitor (PubMed:26138974). kcat is 4745 sec(-1) for conversion of L-lactate to D-lactate. kcat is 1333 sec(-1) for conversion of D-lactate to L-lactate. Homodimer. Induced by L-lactate and repressed by D-lactate. The lactate racemase activity is thus regulated by the L-lactate/D-lactate ratio, under the control of the transcriptional regulator LarR. Makes part of the lar operon (larABCDE). Deletion of this gene leads to a loss of lactate racemase activity. Belongs to the lactate racemase family.