leucine, organic compund, one of the 20 amino acids commonly found in animal proteins. Only the l-stereooisomer appears in mammalian protein. It is one of several essential amino acids needed in the diet; the human body cannot synthesize it from simpler metabolites. Young adults need about 31 mg of this amino acid per day per kilogram (14 mg per lb) of body weight. Leucine can be degraded into simpler compounds by the enzymes of the body. Leucine contributes to the structure of proteins into which it has been incorporated by the tendency of its side chain to participate in hydrophobic interactions. Certain proteins that bind to DNA (see nucleic acid) and may help regulate its activities, posses regions in which leucines are arranged in configurations called leucine zippers. Leucine was isolated from cheese in an impure form in 1819 and from muscle and wool in the crystalline state in 1820. It was named after the Greek word leukos [white], evidently because at that time the purification of a subtance from nature to a white, crystalline state was considered noteworthy. The stucture of leucine was established by laboratory synthesis in 1891. See isoleucine.

One of the essential amino acids, present in most common proteins and particularly abundant in hemoglobin. One of the first amino acids discovered (1819), it is used in biochemical research and as a nutritional supplement.

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Leucine (abbreviated as Leu or L) is an α-amino acid with the chemical formula HO₂CCH(NH₂)CH₂CH(CH₃)₂. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic amino acid.

Biosynthesis

As an essential amino acid, leucine is not synthesized in animals, hence it must be ingested, usually as a component of proteins. It is synthesized in plants and microorganisms via several steps starting from pyruvic acid. The initial part of the pathway also leads to valine. The intermediate α-ketovalerate is converted to α-isopropylmalate and then β-isopropylmalate, which is dehydrogenated to α-ketoisocaproate, which in the final step undergoes reductive amination. Enzymes involved in a typical leucine biosynthesis include

• Acetolactate synthase,
• Acetohydroxy acid isomeroreductase,
• Dihydroxyacid dehydratase,
• α-Isopropylmalate synthase,
• α-Isopropylmalate isomerase,
• Leucine aminotransferase.

Biological Uses

As a dietary supplement, leucine has been found to slow the degradation of muscle tissue by increasing the synthesis of muscle proteins. Leucine is utilized in the liver, adipose tissue, and muscle tissue. In adipose and muscle tissue, leucine is used in the formation of sterols, and the combined usage of leucine in these two tissues is seven times greater than its use in the liver.

Food additive

As a food additive L-Leucine has E number E641 and is classified as a flavour enhancer.

See also

• Photo-reactive leucine

References

External links

• Leucine biosynthesis
• Leucine content in food
• Computational Chemistry Wiki
• Leucine prevents muscle loss in rats
• Leucine helps regulate appetite in rats
• Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects