Oxidation of Ammonia by Nitrosomonas europaea DEFINITIVE "0-TRACER EVIDENCE THAT HYDROXYLAMINE FORMATION INVOLVES

NHzOH, the first intermediate in the oxidation of m+ tonitrite by the nitrifying bacterium, Nitrosomonus europaea, was recovered as the oxime of cyclohexanone. "N, "0-tracer experiments using highly enriched "NH&l and l8O2 yielded oxime that was correspondingly highly enriched (292 atom 76) in these isotopes. These results show that the source of NHzOH is largely or entirely NK', as opposed to hydrazine, which was added to inhibit the further oxidation of NHzOH to nitrite, and that NI&+ yields NHzOH by way of a monooxygenase reaction involving direct insertion of 0 from 0 2 . The oxidation of m+ and NHzOH must be functionally linked in N. europaea, inasmuch as the reducing equivalents required by the monooxygenase to reduce the second atom of O2 to water can arise only through the concomitant oxidation of NHzOH.