Influence of Oxygen Availability

If the interpretation that Carboniferous hyperoxic conditions favored evolution of ani- 

TRUE FERMENTATION VERSUS ANAEROBIC AND AEROBIC RESPIRATION 

For aerobic organisms in the oxic world following the appearance of oxygenic (green plant 

The nitrite formed is either excreted directly or reduced by non-ATP-yielding reactions to ammonia. The enzyme machinery for both processes, nitrate/nitrite respiration and denitrification, is formed only under anaerobic conditions or conditions of low oxygen tension. In fact, the activities of the enzymes involved in dissimila-tory nitrate reduction are strongly inhibited by oxygen. Thus, denitrification and nitrate/nitrite respiration take place only when oxygen is absent or available in insufficient amounts. 

It is now evident that at least two, and probably more, of the four possible reductive steps are coupled to ATP formation in denitrifying bacteria. As may be expected from thermodynamic consideration, this crucial observation implies an ATP yield per mole of glucose similar to that for normal oxidative metabolism (see Gottschalk, 1979, for literature in this area). 

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