Characterization of a Nitrate Reductase from the Chemoautotroph Nitrobacter agiZis*

The energy thus liberated is used in part for the assimilation of carbon dioxide which serves as the sole carbon source for growth. Studies of the biochemistry of Nitrobacter agilis have been mainly limited by the difficulty in obtaining large yields of cells, as has been the case with many of the chemoautotrophs. There has consequently been a relat.ively slow advancement of biochemical research concerning the mechanism of nitrification as well as that of other metabolic pathways in these organisms. Aleem and Alexander (4) have recently devised culture methods for growing the organism in appreciable yields, thus opening the way for studies with cell-free preparations of the bacteria. Most of the subsequent investigations with Nitrobacter have been mainly concerned with the cell-free oxidation of nitrite to nitrate. Aleen and Nason (5) demonstrated that the nitrite-oxidizing activity of these cell-free preparations resides solely in a cytochrome-containing particle designated as nitrite oxidase. Spectral evidence suggested that nitrite oxidation involved the enzymatic transfer of electrons from nitrite to molecular oxygen via cytochrome c and cytochrome al according to the following sequence.