LDHAL6B (L-lactate dehydrogenase A-like 6B) catalyzes the reaction of PYR (pyruvate) and NADH + H+ to form LACT (lactate) and NAD+. The LDHAL6B protein is the inferred product of an open reading frame transcribed in the testis (Wang et al. 2005). Its mitochondrial localization is inferred from the presence of a mitochondrial localization sequence at its amino terminus (Holmes and Goldberg 2009). A physiological role for lactate formation from the abundant pyruvate and NADH expected in rapidly respiring mitochondria is not straightforward to imagine, however.