The Mechanism of Reduction of Nitrates and Nitrites in Processes of Assimilation

The mechanism of reduction of nitrates of the alkali metals to ammonia and the formation of amino nitrogen in biochemical syntheses from inorganic nitrogen compounds have not been explained satisfactorily. Some investigators explain the transformation by assuming a direct reduction of the nitrates to ammonia by action of nascent hydrogen, while others assume an intermediate reduction of the nitrate to nitrite, from which, as the reduction proceeds, ammonia is produced. The exact chemical procedure by which bacteria or molds are able to produce ammonia or nitrites from alkali nitrates also has not been satisfactorily explained. Schimper,l the botanist, has been able to demonstrate experimentally that the reduction of nitrates in green leaves is connected intimately in some manner, not only with the influence of light, but also with the action of iron compounds in the leaves. This observation was so interesting to the writer that it led him to an investigation of the question whether iron actually takes part in the reduction of nitrates by means of bacteria. This work has proved very productive and, as a matter of fact, experiments have shown conclusively that the cholera bacillus, which possesses extraordinary reducing power for nitrates, has the ability to accumulate iron2 in its organism, and its reducing power may possibly be a function, not only of its ability to absorb oxygen by respiration, but also of its iron content. The data revealed through this biological research, which was interrupted by the War and political disturbances in Europe,