Abstract
THE reduction of nitrate is accomplished by cells of very diverse types—plant, animal, and bacterial. A thermolabile catalyst controls the activation of nitrate, though cases are known where apparently nitrate may be reduced by biological means without the intervention of a specific catalyst.1 The distribution of the nitrate oxidase, as the catalyst may be conveniently termed, seems to be very haphazard; it occurs in the livers of most animals, but nitrate reduction in muscle is confined to the rat and guineapig. Among the bacteria, it is absent from obligate anaerobes and aerobes, but it occurs in most faculative anaerobes. With these organisms nitrate serves as an oxidising source and will enable anaerobic growth to occur in its presence.2 The nitrate oxidase is present in B. coli, the ability of which to reduce nitrate to nitrite has been made a test of its presence in biological fluids. The activity of the enzyme is greatly inhibited by traces of hydrogen cyanide,3 but if a suspension of B. coli which has been exposed to quite a high concentration of hydrogen cyanide is well washed with saline the organism regains its ability to activate nitrate.4 The effect of cyanide on nitrate oxidase is thus reversible.
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