The substrate is
hydroxylamine (), a chemical produced biologically by the enzyme
Ammonia monooxygenase. The products of the
catalyzed reaction are debated, but recent work shows compelling evidence for the production of
nitric oxide.[1]
Structural studies
Crystallographic methods show that HAO (PDB code:
1FGJ) is a cross-linked
trimer of polypeptides containing 24
heme cofactors.[2][3]
Reactivity
For many decades the enzyme was thought to catalyze the following reaction:[4]
Recent work in the field, however, reveals that this enzyme catalyzes an entirely different reaction:[1]
Subsequent oxidation of the nitric oxide to nitrite caused by reaction with oxygen accounts for the reactivity previous described by Hooper et al.
Environmental Impact
Nitric oxide, the product of HAO catalysis, is a potent
greenhouse gas.[5] Additionally, the oxidized product of nitric oxide in the presence of oxygen is
nitrite - a common pollutant in
agricultural run-off.
^Cedervall, Peder; Hooper, Alan B.; Wilmot, Carrie M. (2013-09-10). "Structural Studies of Hydroxylamine Oxidoreductase Reveal a Unique Heme Cofactor and a Previously Unidentified Interaction Partner". Biochemistry. 52 (36): 6211–6218.
doi:
10.1021/bi400960w.
ISSN0006-2960.
PMID23952581.
^Igarashi, N.; Moriyama, H.; Fujiwara, T.; Fukumori, Y.; Tanaka, N. (April 1997). "The 2.8 A structure of hydroxylamine oxidoreductase from a nitrifying chemoautotrophic bacterium, Nitrosomonas europaea". Nature Structural Biology. 4 (4): 276–284.
doi:
10.1038/nsb0497-276.
ISSN1072-8368.
PMID9095195.
S2CID1028628.
^Hendrich, Michael P.; Logan, Michael; Andersson, Kristoffer K.; Arciero, Dave M.; Lipscomb, John D.; Hooper, Alan B. (1994-12-01). "The Active Site of Hydroxylamine Oxidoreductase from Nitrosomonas: Evidence for a New Metal Cluster in Enzymes". Journal of the American Chemical Society. 116 (26): 11961–11968.
doi:
10.1021/ja00105a041.
ISSN0002-7863.
Lipscomb JD, Hooper AB (1982). "Resolution of multiple heme centers of hydroxylamine oxidoreductase from Nitrosomonas. 1. Electron paramagnetic resonance spectroscopy". Biochemistry. 21 (17): 3965–72.
doi:
10.1021/bi00260a010.
PMID6289867.
Rees MK (1968). "Studies of the hydroxylamine metabolism of Nitrosomonas europaea. I Purification of hydroxylamine oxidase". Biochemistry. 7 (1): 353–66.
doi:
10.1021/bi00841a045.
PMID5758552.