Protein Synthesis and Degradation

Glutamine plays a significant role in the synthesis of proteins and nonessential amino acids. Glutamine is referred to as competence factor since it stimulates protein synthesis.4 It is an amino group donor in various biosynthetic reactions of purine, pyrimidine, and amino sugar syntheses. Glutamine also serves as a storage and transport form of ammonium and plays a significant role in the removal of excess ammonia by playing a critical part in the urea synthesis process. Glutamine is a regulator of urea synthesis since the enzyme carbomyl phosphate synthetase is allosterically activated by N-acetylglutamate for the utilization of the first nitrogen molecule in the urea synthesis. Glutamine utilization of the cells increases dramatically during hypercatabolic conditions such as trauma and sepsis to fulfill the energy demands and to provide nitrogen for the protein synthesis occurring during these states.12

Glutamine regulates muscle protein levels and has been shown to have antipro-teolytic effects on noncontractile protein components in the rat model.5 Decreasing intramuscluar glutamine concentrations has been shown to increase muscle cata-bolism. 5 Glutamine has also been observed to regulate the myosin heavy-chain synthesis seen in glucocorticoid-induced muscle atrophy.5 Fatigue due to increased exercise can increase overall protein catabolism and lower plasma and muscle concentration of amino acids; glutamine has been observed to play a key role in restoring these amino acid concentrations.5 Glutamine supplementation has been observed to stimulate an increase in muscle protein synthesis, especially immediately after exhaustive exercise.6

Glutamine also plays an important role in the regulation of acid-base balance by allowing the kidneys to excrete an acid load, thereby protecting the body against acidosis, and serves as the most important nitrogen shuttle, supplying nitrogen for metabolic purposes.12 Glutamine is a precursor for the synthesis of nucleic acids. It also plays a role in the synthesis of glutathione, a tripeptide molecule synthesized from glycine, cysteine, and glutamate. Glutathione plays a role in the transport of certain amino acids and in the synthesis of leukotriene (which regulates the inflammation response), and it protects the cells from the harmful effects of free radicals.7

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