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leucine (lo͞oˈsēn), 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.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



aminoisocaproic acid, a mono-amino-monocar-boxylic acid; colorless crystals. Melting point, 293°-295°C (with decomposition); poorly soluble in cold water; molecular weight, 131.18.

Leucine was first isolated in 1820 from muscle tissue. The natural L-leucine is a component of all animal and plant proteins. It is classified as one of the essential amino acids: the carbon skeleton of its precursor, α-ketoisovalerianic acid, is not synthesized in the human or animal body. An absence of leucine in the food results in a negative nitrogen balance and stops growth in children. The daily leucine requirement for adults and infants is 31 mg per kg and 425 mg per kg, respectively. One of the products of leucine breakdown in the body, β-hydroxy-β-methylglutaric acid (in the form of acyl coenzyme A), is an important intermediate compound in the biosynthesis of cholesterol and other steroids. Leucine is used, together with glutamic acid, methionine, and other amino acids, in the treatment of liver diseases, anemias, and some mental disorders.


Meister, A. Biokhimiia aminokislot. Moscow, 1961. (Translated from English.)
Kagan, Z. S. “Biosintez leitsina i ego reguliatsiia u mikroorganizmov i rastenii.” Uspekhi biologicheskoi khimii, 1970, vol. 11, pp. 87–106.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


C6H13O2N A monocarboxylic essential amino acid obtained by hydrolysis of protein-containing substances such as milk.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Chen, the CSO of Creative Biolabs, "to precisely identify leucine and isoleucine is just one step along the path, but an important one."
In this study 48 healthy men aged 72 [+ or -] 1 yr were assigned to one of four groups: 40 g casein, 20 g casein, 20 g casein plus 1.5 g of crystalline leucine, or placebo.
McIntosh, "Spray-dried influenza antigen with trehalose and leucine produces an aerosolizable powder vaccine formulation that induces strong systemic and mucosal immunity after pulmonary administration," Journal of Aerosol Medicine and Pulmonary Drug Delivery, vol.
It could be concluded that the Sn[O.sub.2] growth can be suppressed when synthesized by a sol-gel method assisted with biomimetic assembly using leucine as a biotemplate.
Wiltafsky et al [10] reported that an increase in the SID leucine:valine ratio in diets fed to pigs produced a 3-fold increase in branched-chain [alpha]-keto acid dehydrogenase (BCKDH) activity in the liver but reported no effect of leucine level on the mRNA expression of mitochondrial BCAA transaminase ([BCAT.sub.m]).
"Leucine has been shown to help the body better utilize protein to make lean body mass," explains Jaffe.
The strains isolated from hand surfaces had the highest activity of acid phosphatase (an average of 12.4 nmol) and esterase (an average of 12.1 nmol), and the lowest activity of beta-glucuronidase (an average of 0.1 nmol); while strains isolated from phone surfaces had the highest activity of leucine arylamidase (an average of 10.4 nmol) and acid phosphatase (an average of 12.1 nmol), and the lowest activity was beta-glucuronidase (an average of 0.2 nmol).
The first heptad was manually arranged from four amino acid residues (corresponding amino acid located at g position in the first heptad) before appearance of the first leucine in the bZIP domain.
Further biochemical study with plasma amino acid analysis showed a leucine level of 4163.6 [micro]mol/L (reference values: 42-133.1 [micro]mol/L), isoleucine of 499.8 [micro]mol/L (15.1-74.9 [micro]mol/L), and valine of 784.3 [micro]mol/L (73.6--273.1 [micro]mol/L).
Maple syrup urine disease (MSUD) is an autosomal recessive inherited metabolic disease caused by decreased enzyme activity of branched-chain alpha-ketoacid dehydrogenase complex (BCKDC), responsible for catabolism of leucine (leu), valine (val), and isoleucine (isoleu).
A number of metabolites were identified in the urine, including amino acids such as leucine, alanine, phenylalanine, glycine, and creatine; organic acids such as lactate, acetate, succinate, 2-oxoglutarate, citrate, hippurate, 2-hydroxyvalerate, and cis-aconitate; waste metabolites such as formate, allantoin, dimethylamine, and trimethylamine; and glucose.
The criteria for evaluation of the results of the study were the structural changes of thirteen amino acids: arginine, lysine, tyrosine, phenylalanine, histidine, isoleucine + leucine, methionine, valine, proline, threonine, serine, alanine, glycine [7].