Nitrate reductases

Nitrate reductases are oxidoreductases that catalyze the reduction of nitrate to nitrite . Nitrate reductases play an important role in nitrogen assimilation ( assimilatory nitrate reductases) in plants and nitrate respiration ( dissimilatory nitrate reductases) in bacteria ( denitrification ). Often chlorate can be reduced to chlorite .

The six currently known nitrate reductases can be divided into the following classes based on their electron donor and mechanism:

• NADH nitrate reductase ( EC 1.7.1.1 ) found in plants, bacteria and some other eukaryotes and archaea :  

  ${\displaystyle \mathrm {\ NO_{3}^{-}+NADH+H^{+}\longleftrightarrow \ NO_{2}^{-}+NAD^{+}+H_{2}O} }$

• NAD (P) H nitrate reductase ( EC 1.7.1.2 ) found in plants, bacteria and some saccharomycetes can use both NADH and NADPH:  

  ${\displaystyle \mathrm {\ NO_{3}^{-}+NAD(P)H+H^{+}\longleftrightarrow \ NO_{2}^{-}+NAD(P)^{+}+H_{2}O} }$

• the NADPH nitrate reductase ( EC  1.7.1.3 ) found in many fungi :

  ${\displaystyle \mathrm {\ NO_{3}^{-}+NADPH+H^{+}\longleftrightarrow \ NO_{2}^{-}+NADP^{+}+H_{2}O} }$

• the quinone nitrate reductase ( EC  1.7.5.1 ) found in some bacteria :

  ${\displaystyle \mathrm {\ NO_{3}^{-}+Chinol\longleftrightarrow \ NO_{2}^{-}+Chinon+H_{2}O} }$

• the ferredoxin nitrate reductase ( EC  1.7.7.2 ) found in many bacteria :

  ${\displaystyle \mathrm {\ NO_{3}^{-}+Ferredoxin_{red.}\longleftrightarrow \ NO_{2}^{-}+Ferredoxin_{ox.}+H_{2}O} }$

• the cytochrome nitrate reductase found in some bacteria ( EC  1.9.6.1 ):

  ${\displaystyle \mathrm {\ NO_{3}^{-}+2\ H^{+}+2\ Acceptor_{red}\longleftrightarrow \ NO_{2}^{-}+2\ Acceptor_{ox}^{+}} }$

Web links

• Importance of nitrate and its metabolism for humans
• Nitrate Reductase - A Magical Enzyme? (English)