<br/>Nitrification, the oxidation of ammonia to nitrite and nitrate, is a key entry point for fixed nitrogen to return to the atmosphere as dinitrogen. Nitrification is the root of tremendous economic loss in agriculture as well as a major ecological hazard via nitrogenous eutrophication. Molecular details concerning the elementary, multi-electron chemical steps whereby ammonia is oxidized to hydroxylamine and ultimately to nitrite remain elusive. This may be attributable in part to the difficulty associated with accessing sufficient quantities of relevant enzymes for biophysical characterization. Nevertheless, such insights are attractive because they hold the promise of inspiring novel, green chemical methods for difficult bond activations and multi-electron transformations. In our recent work, we revised the biochemistry of hydroxylamine oxidoreductase, showing that this enzyme's product is nitric oxide, contrary to long-held dogma that held that this product was nitrite. Because ammonia oxidizing bacteria stoichiometrically convert ammonia/ammonium to nitrite, and because this nitrite cannot be the product of abiotic reactivity of nitric oxide with dioxygen, at least one other enzyme must be operative. This talk will make the case for the identity of at least one such nitric oxide-oxidizing enzyme in ammonia oxidizing bacteria, with lines of evidence drawn from transcriptomics, enzyme kinetics, and spectroscopy.

A missing link from nitric oxide to nitrite in ammonia oxidizing bacteria

255th National Meeting (2018)

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