Catalyzes the conversion of lactate to pyruvate. (S)-lactate + NAD(+) = H(+) + NADH + pyruvate Activated by citrate at pH 5. Allosterically activated by fructose 1,6-bisphosphate (FBP) at pH from 5.8 to 7.2. Optimum pH is 5 and 6.7 with citrate and fructose 1,6-bisphosphate (FBP) as activator, respectively. Fermentation; pyruvate fermentation to lactate; (S)-lactate from pyruvate: step 1/1. Homotetramer. Belongs to the LDH/MDH superfamily. LDH family.