NADPH-nitrate reductase assimilatory

Nitrate reductase (NADH) [EC 1.6.6.1], also known as assimilatory nitrate reduetase, eatalyzes the reaction of NADH with nitrate to produee NAD+, nitrite, and water. This enzyme uses FAD or FMN, heme, and a molybdenum ion as eofaetors. (2) Nitrate reductase (NAD(P)H) [EC 1.6.6.2], also known as assimilatory nitrate reduetase, eatalyzes the reaetion of NAD(P)H with nitrate to produee NAD(P)+, nitrite, and water. This enzyme uses FAD or FMN, heme, and a molybdenum ion as eofaetors. (3) Nitrate reductase (NADPH) [EC 1.6.6.3] eatalyzes the reaetion of NADPH with nitrate to produee NADP+, nitrite, and water. This enzyme uses FAD, heme, and a molybdenum ion as cofactors. (4) Nitrate reduetase (eytoehrome) [EC 1.9.6.1] catalyzes the reaetion of nitrate with ferroeytochrome to produce nitrite and ferrieytoehrome. (5) Nitrate reductase (ac-eeptor) [EC 1.7.99.4], also known as respiratory nitrate... 

Many species of bacteria also have an assimilatory nitrite reductase which is located in the cytoplasm. There is relatively little known about such enzymes but the electron donor is throught to be NADPH and the active site again has siroheme (Cole, 1988). The assimilatory nitrite reductases of both plants and bacteria use nitrite that is provided as the product of the assimilatory nitrate reductases. Nitrate is a very common natural N source for plant and bacterial growth. 

In all photoautotrophs, reduction of NOj" to NH4 is achieved in two distinct enzymatic steps (Campbell, 2001). First, assimilatory nitrate reductase (NR) catalyzes the two electron reduction from NOj" to NO2. NR is a large soluble cytoplasmic enzyme with FAD (flavin adinine dinucleotide), an iron-containing cytochrome and molybdopterin prosthetic groups, and requires NADH and/or NADPH as an electron donor (Guerrero et al, 1981). Functional NR is in the form of a homodimer and therefore requires two atoms of iron per enzyme. Following transport into the chloroplast, NO2 undergoes a 6 e reduction to NH4 via assimilatory nitrite reductase (NiR). NiR, a soluble chloroplastic enzyme, contains five iron atoms per active enzyme molecule, and requires photosynthetically reduced ferredoxin as an electron donor (Guerrero et al., 1981). 

---