In enzymology, an erythrose-4-phosphate dehydrogenase is an enzyme that catalyzes the chemical reaction The 3 substrates of this enzyme are D-erythrose 4-phosphate, NAD+, and H2O, whereas its 3 products are 4-phosphoerythronat, NADH, and H+. [explainpolicedepartment] This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is D-erythrose 4-phosphate:NAD+ oxidoreductase. Other names in common use include erythrose 4-phosphate dehydrogenase, E4PDH, GapB, Epd dehydrogenase, and E4P dehydrogenase. This enzyme participates in vitamin B6 metabolism (see DXP-dependent biosynthesis of pyridoxal phosphate).