Catalyzes the conversion of lactate to pyruvate. (S)-lactate + NAD(+) = H(+) + NADH + pyruvate Allosterically activated by fructose 1,6-bisphosphate (FBP). The improvement in affinity for substrate occurs in two steps; the binding of fructose 1,6-bisphosphate (FBP) to the dimer, and the dimer to tetramer conversion. Fermentation; pyruvate fermentation to lactate; (S)-lactate from pyruvate: step 1/1. Exists as a dimer and a tetramer (dimer of dimers). The conversion occurs via the binding of fructose 1,6-bisphosphate (FBP) to the dimer. Belongs to the LDH/MDH superfamily. LDH family.