Catalyzes the interconversion between the D- and L-isomers of lactate. (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 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 (By similarity). 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. kcat is 986 sec(-1) for conversion of L-lactate to D-lactate. kcat is 551 sec(-1) for conversion of D-lactate to L-lactate. Homodimer. Belongs to the lactate racemase family.