Keywords:

Abstract:

<p>Ammonia oxidizing archaea (AOA) are among the most abundant microorganisms on earth and are known to be a major source of nitrous oxide (NO) emissions, although biochemical origins of this NO remain unknown. Enzymological details of AOA nitrogen metabolism are broadly unavailable. We report the recombinant expression, purification, and characterization of a multicopper oxidase, Nmar_1354, from the AOA . We show that Nmar_1354 selectively produces nitroxyl (HNO) by coupling the oxidation of the obligate nitrification intermediate hydroxylamine (NHOH) to dioxygen (O) reduction. This HNO undergoes several downstream reactions, although the major fates are production of N via reaction with NHOH and dimerization with itself to yield NO. These results afford one plausible enzymatic origin for NO release by AOA. Moreover, these results reveal a physiologically relevant enzymatic reaction for producing HNO, an enigmatic nitrogen oxide speculated to be operative in cellular signaling and in energy transduction.</p>