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Abstract
Ammonia oxidizing archaea (AOA) are among the most abundant microorganisms on earth and are known to be a major source of oceanic nitrous oxide (N2O) emissions, although biochemical origins of this N2O remain unknown. Enzymological details of AOA nitrogen metabolism are broadly unavailable. We report the recombinant expression, purification, and characterization of a multicopper oxidase (MCO), Nmar_1354, from the AOA Nitrosopumilus maritimus. We show that Nmar_1354 selectively produces nitroxyl (HNO) by coupling the oxidation of the obligate nitrification intermediate hydroxylamine (NH2OH) to dioxygen (O2) reduction. This HNO undergoes several downstream reactions, although a significant fraction rapidly dimerizes to yield N2O. These results afford a possible enzymatic origin of AOA-derived N2O and reveal a unique enzymatic reaction for producing HNO.
