Enzymatic activity of Nitrosomonas extracts.

The sole energy-yielding reaction of the autotrophic nitrifying bacterium Nitrosomonas europaea involves the conversion of ammonium to nmtrite. As early as 1926, Kluyver and Donker postulated that the six electron oxidation proceeds with the intermediary formation of hydroxylamine and hyponitrous acid. Only recently have there been any studies of the biochemical mechanism of chemoautotrophic ammonium oxidation. Hydroxylamine is metabolized by intact cells of this organism and is rapidly and stoichiometrically converted to nitrite (Hofman and Lees, 1953; Engel and Alexander, 1958). Imshenetsky and Ruban (1954, 1956) have reported that autolysates of a Nitrosomonas sp. prepared by incubation at 40 C for 24 hr brought about a slow disappearance of ammonium and hydroxylamine in periods of about 5 days. The disappearance of substrate did not result in the formation of appreciable amounts of the nitrite end-product, possibly suggesting the accumulation of some intermediate at the +1 oxidation state of nitrogen although other explanations are possible. With the availability of relatively large amounts of active cellular material, a reinvestigation of nitrification by enzyme extracts was in'itiated.