Author
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SURYAWAN, AGUS - Children'S Nutrition Research Center (CNRC) |
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DAVIS, TERESA - Children'S Nutrition Research Center (CNRC) |
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Submitted to: Book Chapter
Publication Type: Book / Chapter Publication Acceptance Date: 10/1/2014 Publication Date: 1/20/2015 Citation: Suryawan, A., Davis, T.A. 2015. Enteral leucine and protein synthesis in skeletal and cardiac muscle. In: Rajendram, R., Preedy, V.R, Patel, V.B., editors. Branched Chain Amino Acids in Clinical Nutrition. 1st edition. New York, NY: Springer. p. 197-210. Interpretive Summary: Protein synthesis is the creation of new proteins that are needed for growth and maintenance. Leucine is an amino acid that acts as a stimulator of skeletal and cardiac muscle protein synthesis. However, the mechanism by which leucine stimulates protein synthesis is not completely known. Studies show that in order to stimulate protein synthesis, leucine has to activate components of protein-synthetic pathways and one of the major components is called mechanistic target of rapamycin complex 1 (mTORC1). The vast majority of leucine studies were done in short-term studies. Thus, to determine beneficial effects of leucine for human health, long-term studies are warranted. Technical Abstract: There are three members of the Branch Chain Amino Acids: leucine, isoleucine, and valine. As essential amino acids, these amino acids have important functions which include a primary role in protein structure and metabolism. It is intriguing that the requirement for BCAA in humans comprise about 40–45 % of the total essential amino acids. However, human deficiency of the BCAA usually does not occur due to a high percentage of these amino acids (up to 50 %) in the food supply. Another unique property of the BCAA is that, unlike other amino acids, the majority of BCAA are metabolized in muscle and other nonsplanchnic tissues suggesting that BCAA metabolism is important in these tissues. There are two steps in the metabolic pathway of BCAA . The first step, which is reversible and catalyzed by branched-chain amino acid amino transferase(BCAT), is transamination of BCAA (leucine, isoleucine, and valine)to form their respective a-keto acids (a- ketoisocaproate, a-keto-beta-methylvalerate, and a-ketoisovalerate). The second step is an irreversible catabolic process catalyzed by the branched-chain a-keto acid dehydrogenase (BCKD) complex which involves oxidative decarboxylationof all of the branched-chain keto acids. In the second step, the carbon skeletons of the BCAA are committed to be degraded for substrates of the tricarboxylic acid (TCA) cycle. Consistent with the notion that BCAA are metabolized in nonsplanchnic tissues, the abundance and the activation of BCAT and BCKD are detectable in nonsplanchnic peripheral tissues from several species including rats, monkeys, and humans. |
