Fig. 2

Ammonia produced by amino acid decomposition is transported in two ways: 1) in the form of glutamine. Under the catalyzation of glutamine synthetase (GS), the reaction of ammonia and glutamate produces glutamine, which is transported to the liver through blood, and decomposed to glutamate and ammonia via catalyzation by glutaminase. The ammonia then enters the urea synthesis process; 2) in the form of alanine. Pyruvic acid produced by glycolysis in muscles reacts with ammonia via the catalyzation of transaminases, producing alanine. Alanine is transported to the liver through blood and reacts with α-KG to produce pyruvic acid and glutamate via catalyzation by alanine transaminase. Glutamate produced in both ways is deaminated and the generated ammonia enters the urea synthesis process and is further removed from the body. α-KG, alpha-ketoglutaric acid; TCA cycle, tricarboxylic acid cycle; GDH, glutamate dehydrogenase