Nitrate reductase (NR)

Nitrate reductase (NR) is a molybdoenzyme that catalyzes the key two-electron reduction of nitrate (NO3-) to nitrite (NO2-), serving as the first step in nitrate assimilation in plants, algae, fungi, and bacteria, or in dissimilatory processes in prokaryotes.[1][3][4][7] It belongs to the DMSO reductase family and contains a molybdenum cofactor (Mo-MPT or Mo-bisMGD), along with additional prosthetic groups like FAD, heme, and iron-sulfur clusters that facilitate electron transfer from NAD(P)H or quinol donors to the active site.[1][2][3][4] In eukaryotic assimilatory NR, the enzyme is a homodimeric cytosolic protein with distinct domains including Mo-MPT, cytochrome b, and NAD(P)H-binding regions, regulated post-translationally via serine phosphorylation and 14-3-3 protein binding.[1][4] Prokaryotic forms include membrane-bound (Nar) heterotrimers involved in anaerobic respiration and proton motive force generation, and periplasmic (Nap) heterodimers for nitrite production under microaerophilic conditions.[3][4] Crystal structures from organisms like Escherichia coli (NarGHI) and Desulfovibrio desulfuricans (NapA) reveal a conserved Mo coordination sphere with sulfur ligands and oxygen/sulfur terminals, enabling mechanisms involving Mo(IV) to Mo(VI) redox cycles and oxygen atom transfer.[3][4][5] While essential for nitrogen metabolism and crop productivity, NR is not a established therapeutic target in humans, lacking direct roles in mammalian physiology or common disease pathologies.[1][3][4]

Other names

NAR (membrane-bound nitrate reductase)NAP (periplasmic nitrate reductase)Nas (assimilatory nitrate reductase)