"PHDGH catalyzes the first reaction of de novo serine biosynthesis, producing 3-phosphohydroxypyruvate by NAD+-coupled oxidation of 3-phosphoglycerate (3PG). The PHGDH reaction is reversible and, under standard conditions, thermodynamically favors the direction from 3-phosphohydroxypyruvate to 3PG. In cells engaged in serine synthesis, the reaction is driven toward 3-phosphohydroxypyruvate due to its consumption by downstream pathway steps." [PMID:25406093]