Electron transfer during the oxidation of ammonia by the chemolithotrophicbacterium Nitrosomonas europaea

The combined action of ammonia monooxygenase, AMO, (NH3+2e(-)+O-2 --> NH2OH ) and hydroxylamine oxidoreductase, HAO, (NH2OH+H2O --> HNO2+4e(-)+4H(+)) a ccounts for ammonia oxidation in Nitrosomonas europaea. Pathways for electr ons from HAO to O-2, nitrite, NO, H2O2 or AMO are reviewed and some recent advances described. The membrane cytochrome c(M)552 is proposed to particip ate in the path between HAO and ubiquinone. A brl complex is shown to media te between ubiquinol and the terminal oxidase and is shown to be downstream of HAO. A novel, red, low-potential, periplasmic copper protein, nitrosocy anin, is introduced. Possible mechanisms for the inhibition of ammonia oxid ation in cells by protonophores are summarized. Genes for nitrite- and NO-r eductase but not N2O or nitrate reductase are present in the genome of Nitr osomonas. Nitrite reductase is not repressed by growth on O-2, the flux of nitrite reduction is controlled at the substrate level. (C) 2000 Elsevier S cience B.V. All rights reserved.