THE BIOCHEMICAL-CHARACTERIZATION OF A NOVEL NON-HEME-IRON HYDROXYLAMINE OXIDASE FROM PARACOCCUS-DENITRIFICANS GB17

The characterization of the hydroxylamine oxidase from the heterotroph ic nitrifier Paracoccus denitrificans GB17 indicates the enzyme to be entirely distinct from the hydroxylamine oxidase from the autotrophic nitrifier Nitrosomonas europaea. Hydroxylamine oxidase from P. denitri ficans contains three to five non-haem, non-iron-sulphur iron atoms as prosthetic groups, predominantly co-ordinated by carboxylate ligands. The interaction of the enzyme with the electron-accepting proteins cy tochrome c(550) and pseudoazurin is mainly hydrophobic. The catalytic mechanism of hydroxylamine oxidase from P. denitrificans is different from the enzyme from N. europaea because the production of nitrite by the former requires molecular oxygen. Under anaerobic conditions the e nzyme makes nitrous oxide as a sole product.