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. Author manuscript; available in PMC: 2015 Feb 2.
Published in final edited form as: Annu Rev Physiol. 2007;69:317–340. doi: 10.1146/annurev.physiol.69.040705.142215

Figure 1.

Figure 1

Proximal tubule ammoniagenesis. Ammonia is produced from glutamine (Gln) as a result of proximal tubule ammoniagenesis. Glutamine is transported across both the apical and basolateral plasma membranes and then transported into mitochondria. The enzyme glutaminase (GA) is the first step in ammoniagenesis, and glutamate dehydrogenase (GDH) results in the production of the second NH4+ molecule. Metabolism of α-ketoglutarate (αKG) leads to the production of the first of two HCO3− ions. Further metabolism in the cytoplasm results in the production of a second HCO3−. Thus, complete metabolism of each glutamine produces two NH4+ and two HCO3− ions. Blue circles denote transport proteins. Dotted gray line indicates the minor component of transport, and the solid gray line indicates the major component of transport. Other abbreviations used: NHE-3, Na+/H+ exchanger type 3; OAA, oxaloacetic acid; PEP, phosphoenolpyruvate; PEPCK, phosphoenolpyruvate carboxykinase; TCA, tricarboxylic acid cycle.