J. Biol. Chem., Vol. 258, Issue 6, 3587-3591, Mar, 1983
15N-tracer and NMR studies on the pathway of denitrification. Evidence against trioxodinitrate but for nitroxyl as an intermediate
EA Garber, S Wehrli and TC Hollocher
The effects of four species of denitrifying bacteria on the conversion of
[15N]nitrite to trioxodinitrate (HN2O3-) and N2O and of trioxodinitrate to
N2O were studied. For all species, the N2O produced in the presence of
[15N]nitrite and trioxodinitrate was isotopically randomized throughout the
period of incubation and was not composed at the outset predominantly of
14N2O or 14N2O plus 15N2O. The N2O produced was also heavily enriched in
15N at times when the trioxodinitrate pool was only weakly enriched in 15N.
By 15N NMR, the N(2) position, but not the N(1) position, of
trioxodinitrate was found to become progressively labeled with 15N during
incubation with [15N]nitrite. These results argue that (a) the N-N bond of
trioxodinitrate is not preserved in its conversion to N2O, (b)
trioxodinitrate can be neither a free nor enzyme- bound intermediate in
denitrifying bacteria, and (c) the pathways from nitrite and
trioxodinitrate involve a common mononitrogen intermediate. The conclusion
that this intermediate is probably nitroxyl (HNO), at least with Paracoccus
denitrificans and Pseudomonas stutzeri, provides indirect evidence that N-N
bond formation in denitrification can occur through the dimerization of
nitroxyl.
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