ⓘ Nitrous-oxide reductase. In enzymology, a nitrous oxide reductase also known as nitrogen:acceptor oxidoreductase is an enzyme that catalyzes the final step in b ..


ⓘ Nitrous-oxide reductase

In enzymology, a nitrous oxide reductase also known as nitrogen:acceptor oxidoreductase is an enzyme that catalyzes the final step in bacterial denitrification, the reduction of nitrous oxide to dinitrogen.

N 2 O + 2 reduced cytochome c ⇌ N 2 + H 2 O + 2 cytochrome c

It plays a critical role in preventing release of a potent greenhouse gas into the atmosphere.


1. Function

N 2 O is an inorganic metabolite of the prokaryotic cell during denitrification. Thus, denitrifiers comprise the principal group of N 2 O producers, with roles played also by nitrifiers, methanotrophic bacteria, and fungi. Among them, only denitrifying prokaryotes have the ability to convert N 2 to N 2. Conversion of N 2 O into N 2 is the last step of a complete nitrate denitrification process and is an autonomous form of respiration. N 2 O is generated in the denitrifying cell by the activity of respiratory NO reductase. Some microbial communities have only capability of N 2 O reduction to N 2 and does not have the other denitrification pathways such communities are known as nitrous oxide reducers. Some denitrifiers do not have complete denitrification with end product N 2 O


2. Structure

Nitrous-oxide reductase is a homodimer that is located in the bacterial periplasm. X-ray structures of the enzymes from Pseudomonas nautica and Paracoccus denitrificans have revealed that each subunit MW=65 kDa is organized into two domains. One cupredoxin-like domain contains a binuclear copper protein known as Cu A.

The second domain comprises a 7-bladed propeller of β-sheets that contains the catalytic site called Cu Z, which is a tetranuclear copper-sulfide cluster. The distance between the Cu A and Cu Z centers within a single subunit is greater than 30Å, a distance that precludes physiologically relevant rates of intra-subunit electron transfer. However, the two subunits are orientated "head to tail" such that the Cu A center in one subunit lies only 10 Å from the Cu Z center in the second ensuring that pairs of redox centers in opposite subunits form the catalytically competent unit. The Cu A center can undergo a one-electron redox change and hence has a function similar to that in the well-known aa 3 -type cytochrome c oxidases EC where it serves to receive an electron from soluble cytochromes c.


3. Inhibitors

Acetylene is the most specific inhibitor of nitrous-oxide reductase. Other inhibitors include azide anion, thiocyanate, carbon monoxide, iodide, and cyanide.

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