Branched-chain amino acid

A branched-chain amino acid is leucine, isoleucine, or valine, protein-building amino acids with branched aliphatic side chains that humans must obtain from food.

Leucine: An essential amino acid with a branched aliphatic side chain and a strong role in regulating protein synthesis. One of the three members, leucine is especially notable for activating mTORC1.
Branched-chain aminotransferase: An enzyme that transfers an amino group from a branched-chain amino acid to an acceptor molecule. It catalyzes the first step in branched-chain amino acid breakdown.
Protein synthesis: The cellular process that uses genetic instructions to assemble amino acids into proteins. Branched-chain amino acids provide residues for new proteins, especially in muscle.
Leucine threshold hypothesis: The proposal that a sufficient leucine dose is needed to maximally stimulate muscle protein synthesis after eating. It offers a mechanism for leucine-rich meals, but the threshold varies with age and meal composition.
Isoleucine: An essential amino acid with a branched aliphatic side chain and both glucogenic and ketogenic metabolic products. It shares the group’s defining structure but differs from leucine in its metabolic fate.
Branched-chain alpha-keto acid dehydrogenase complex: A mitochondrial enzyme complex that oxidatively decarboxylates branched-chain amino acid derivatives. Its activity commits the first breakdown products to further oxidation.
Dietary supplement: A product taken orally to add nutrients or other substances to the diet. Branched-chain amino acid supplements are marketed for exercise and recovery, though benefits depend on context.
Muscle protein synthesis: The cellular production of muscle proteins from amino acids. Whether extra branched-chain amino acids meaningfully increase this process remains context-dependent.
Valine: An essential amino acid with a branched aliphatic side chain and glucogenic metabolic products. It completes the trio and is metabolized differently from leucine and isoleucine.
mTORC1: A protein kinase complex that integrates nutrient and growth signals to regulate cell growth and metabolism. Leucine can activate this nutrient-sensing complex and promote protein synthesis.

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