Nitrogen Metabolism and the Urea Cycle Overview of the flow of nitrogen in the biosphere. Nitrogen, nitrites and nitrates are acted upon by bacteria (nitrogen fixation) and plants and we assimilate these compounds as protein in our diets. Ammonia incorporation in animals occurs through the actions of glutamate dehydrogenase and glutamine synthetase. Glutamate plays the central role in mammalian nitrogen flow, serving as both a nitrogen donor and nitrogen acceptor.
Figure 5.5 Nitrogen metabolism pathways within the human body between the liver, muscle, and kidney cells. (A) Alanine cycle, (B) citric acid cycle, (C) urea cycle, (D) creatine phosphate, and (E) nitrate metabolism.: