Nitrification comprises primary metabolisms whereby certain bacteria and archae selectively convert ammonia to nitrite and nitrate in order to generate cellular reducing equivalents. Both ammonia oxidizing archaea (AOA) and bacteria (AOB) initiate nitrification through the selective hydroxylation of ammonia to hydroxylamine using an integral membrane copper monooxygenase called ammonia monooxygenase (AMO). Hydroxylamine then serves as the source of net reducing equivalents for the cell. AOB oxidize hydroxylamine with the multi-heme enzyme hydroxylamine oxidoreductase (HAO), while the means by which hydroxylamine is oxidized by AOA remains unknown. For almost a decade, our group has carried out spectroscopic, kinetics, and macromolecular structural studies to elucidate the elementary chemical steps involved in nitrification. Key findings to date include the identification of nitric oxide as an obligate intermediate in bacterial nitrification and the identification of vital proton-transfer architecture and its enforcement via heme-protein post-translational cross-linking. This lecture will discuss the aforementioned discoveries as well as sharing current progress toward understanding the reactivity of AMO and identifying the hydroxylamine-oxidizing machinery in AOA.

Updated perspectives on biology's use of fixed nitrogen as cellular fuel

ACS Spring Meeting 2021

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