N2O is an inorganic metabolite of theprokaryotic cell during denitrification. Thus,denitrifiers comprise the principal group of N2O producers, with roles played also by nitrifiers,methanotrophic bacteria, andfungi. Among them, only denitrifying prokaryotes have the ability to convert N2O to N2.[3] Conversion of N2O into N2 is the last step of a complete nitrate denitrification process and is an autonomous form of respiration. N2O is generated in the denitrifying cell by the activity of respiratoryNO reductase.[4] Some microbial communities only have the capability of N2O reduction to N2 and do not possess the other denitrification pathways. Such communities are known as nitrous oxide reducers.[5] Some denitrifiers do not have complete denitrification with end product N2O[6]
Nitrous-oxide reductase is ahomodimer that is located in the bacterial periplasm. X-ray structures of the enzymes fromPseudomonas nautica andParacoccus denitrificans have revealed that each subunit (MW=65 kDa) is organized into two domains.[7] One cupredoxin-like domain contains a binuclearcopper protein known as CuA.
The second domain comprises a 7-bladedpropeller of β-sheets that contains the catalytic site called CuZ, which is a tetranuclear copper-sulfidecluster.[8] The distance between the CuA and CuZ centers within a single subunit is greater than 30Å, a distance that precludes physiologically relevant rates of intra-subunitelectron transfer. However, the two subunits are orientated "head to tail" such that the CuA center in one subunit lies only 10 Å from the CuZ center in the second ensuring that pairs of redox centers in opposite subunits form the catalytically competent unit.[9] The CuA center can undergo a one-electronredox change and hence has a function similar to that in the well-known aa3-typecytochromec oxidases (EC1.9.3.1) where it serves to receive an electron from soluble cytochromesc.[10]
^Schneider, Lisa K.; Wüst, Anja; Pomowski, Anja; Zhang, Lin; Einsle, Oliver (2014). "Chapter 8.No Laughing Matter: The Unmaking of the Greenhouse Gas Dinitrogen Monoxide by Nitrous Oxide Reductase". In Peter M.H. Kroneck and Martha E. Sosa Torres (ed.).The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment. Metal Ions in Life Sciences. Vol. 14. Springer. pp. 177–210.doi:10.1007/978-94-017-9269-1_8.ISBN978-94-017-9268-4.PMID25416395.
^Zumft WG (January 2005). "Nitric oxide reductases of prokaryotes with emphasis on the respiratory, heme-copper oxidase type".J. Inorg. Biochem.99 (1):194–215.doi:10.1016/j.jinorgbio.2004.09.024.PMID15598502.
^Pomowski, A., Zumft, W. G., Kroneck, P. M. H., Einsle, O., "N2O binding at a [lsqb]4Cu:2S copper-sulphur cluster in nitrous oxide reductase", Nature 2011, 477, 234.doi:10.1038/nature10332
^Hill BC (April 1993). "The sequence of electron carriers in the reaction of cytochrome c oxidase with oxygen".J. Bioenerg. Biomembr.25 (2):115–20.doi:10.1007/bf00762853.PMID8389744.S2CID45975377.
