Lactate Dehydrogenase (LDH), which catalyzes the inter-conversion of pyruvate and lactate.

Mammalian lactate dehydrogenase (LDH) comprises three major families of conserved enzymes that catalyse the reversible interconversion of pyruvate and lactate, a key metabolic step in glycolysis and other metabolic pathways. At least five LDH tetrameric isozymes are reported in somatic mammalian tissues, comprising LDHA and LDHB subunits, whereas LDHC₄ is found only in mature testis and spermatozoa, where it is required for male fertility. Lactate dehydrogenase catalyzes the interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD⁺. At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased. Dihydroorotate dehydrogenase (DHODH) is a key enzyme that catalyzes the oxidation of dihydroorotate (DHO) to produce orotate, a key step in pyrimidine biosynthesis.