(S)-lactate + NAD(+) = H(+) + NADH + pyruvate Fermentation; pyruvate fermentation to lactate; (S)-lactate from pyruvate: step 1/1. Testis specific. Higher expression level in adult testis as compared to 6-week-old fetal testis. Belongs to the LDH/MDH superfamily. LDH family. It is uncertain whether Met-1 or Met-50 is the initiator.