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Leucine is a branched-chain
Branched-chain amino acids
A branched-chain amino acid is an amino acid having aliphatic side-chains with a branch...

 α-amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 HO2CCH(NH2)CH2CH(CH3)2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded
Genetic code
The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....

 by six codons (UUA, UUG, CUU, CUC, CUA, and CUG) and is a major component of the subunits in ferritin
Ferritin is a ubiquitous intracellular protein that stores iron and releases it in a controlled fashion. The amount of ferritin stored reflects the amount of iron stored. The protein is produced by almost all living organisms, including bacteria, algae and higher plants, and animals...

, astacin
In molecular biology, astacin is a family of metallopeptidases. These metallopeptidases belong to the MEROPS peptidase family M12, subfamily M12A...

 and other 'buffer' protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s. Leucine is an essential amino acid
Essential amino acid
An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs. conditional essentiality in humans:...



As an essential amino acid, leucine is unable to be synthesised by animals. Consequently, it must be ingested, usually as a component of proteins. In plants and microorganisms, leucine is synthesised from pyruvic acid
Pyruvic acid
Pyruvic acid is an organic acid, a ketone, as well as the simplest of the alpha-keto acids. The carboxylate ion of pyruvic acid, CH3COCOO−, is known as pyruvate, and is a key intersection in several metabolic pathways....

 by a series of enzymes:
  • Acetolactate synthase
    Acetolactate synthase
    The acetolactate synthase enzyme is a protein found in plants and micro-organisms. ALS catalyzes the first step in the synthesis of the branched-chain amino acids ....

  • Acetohydroxy acid isomeroreductase
    -Examples:* 5-alpha reductase* Dihydrofolate reductase* HMG-CoA reductase* Methemoglobin reductase* Ribonucleotide reductase* Thioredoxin reductase* E. coli nitroreductase* Methylenetetrahydrofolate reductase...

  • Dihydroxyacid dehydratase
  • α-Isopropylmalate synthase
    In biochemistry, a synthase is an enzyme that catalyses a synthesis process.Following the EC number classification, they belong to the group of ligases, with lyases catalysing the reverse reaction....

  • α-Isopropylmalate isomerase
    In biochemistry, an isomerase is an enzyme that catalyzes the structural rearrangement of isomers. Isomerases thus catalyze reactions of the formwhere B is an isomer of A.-Nomenclature:...

  • Leucine aminotransferase

Synthesis of the small, hydrophobic amino acid Valine
Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...

 also includes the initial part of this pathway.


Leucine is utilized in the liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, adipose tissue
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...

, and muscle tissue. In adipose and muscle tissue, leucine is used in the formation of sterol
Sterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol...

s, and the combined usage of leucine in these two tissues is seven times greater than its use in the liver.

Leucine is the only dietary amino acid that has the capacity to stimulate muscle protein synthesis. As a dietary supplement, leucine has been found to slow the degradation of muscle tissue by increasing the synthesis of muscle proteins in aged rats. While once seen as an important part of the three branch chained amino acids in sports supplements, leucine has since earned more attention on its own as a catalyst for muscle growth and muscular insurance. Supplement companies once marketed the "ideal" 2:1:1 ratio of leucine, iso-leucine and valine; but with furthered evidence that leucine is the most important amino acid for muscle building, it has become much more popular as the primary ingredient in dietary supplements.

Leucine potently activates the mammalian target of rapamycin
Mammalian target of rapamycin
The mammalian target of rapamycin also known as mechanistic target of rapamycin or FK506 binding protein 12-rapamycin associated protein 1 is a protein which in humans is encoded by the FRAP1 gene...

In chemistry and biochemistry, a kinase is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates, a process referred to as phosphorylation. Kinases are part of the larger family of phosphotransferases...

 that regulates cell growth
Cell growth
The term cell growth is used in the contexts of cell development and cell division . When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two "daughter cells"...

. Infusion of leucine into the rat brain has been shown to decrease food intake and body weight via activation of the mTOR pathway.

Leucine toxicity, as seen in decompensated Maple Syrup Urine Disease
Maple syrup urine disease
Maple syrup urine disease , also called branched-chain ketoaciduria, is an autosomal recessive metabolic disorder affecting branched-chain amino acids. It is one type of organic acidemia...

 (MSUD), causes delirium
Delirium or acute confusional state is a common and severe neuropsychiatric syndrome with core features of acute onset and fluctuating course, attentional deficits and generalized severe disorganization of behavior...

 and neurologic compromise, and can be life-threatening.

In yeast genetics, mutants with a defective gene for leucine synthesis (leu2) are transformed with a plasmid that contains a working leucine synthesis gene (LEU2) and grown on minimal media. Leucine synthesis then becomes a useful selectable marker.

Dietary aspects

Food sources of Leucine
Food g/100g
Soy protein concentrate  4.917
Soybeans, mature seeds, raw 2.97
Beef is the culinary name for meat from bovines, especially domestic cattle. Beef can be harvested from cows, bulls, heifers or steers. It is one of the principal meats used in the cuisine of the Middle East , Australia, Argentina, Brazil, Europe and the United States, and is also important in...

, round, top round, separable lean and fat, trimmed to 1/8" fat, select, raw
The peanut, or groundnut , is a species in the legume or "bean" family , so it is not a nut. The peanut was probably first cultivated in the valleys of Peru. It is an annual herbaceous plant growing tall...

Salami is cured sausage, fermented and air-dried meat, originating from one of a variety of animals. Historically, salami has been popular among Southern European peasants because it can be stored at room temperature for periods of up to 10 years, supplementing a possibly meager or inconsistent...

, Italian, pork
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, salmon, pink, raw
Wheat germ  1.571
Almonds  1.488
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

, broilers or fryers, thigh, meat only, raw
Chicken egg, yolk, raw, fresh 1.40
The common oat is a species of cereal grain grown for its seed, which is known by the same name . While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed...

Beans, pinto, cooked 0.765
Lentils, cooked 0.654
The chickpea is a legume of the family Fabaceae, subfamily Faboideae...

, cooked
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

, yellow
Cow milk, whole, 3.25% milk fat 0.27
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...

, brown, medium-grain, cooked
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

, human, mature, fluid


Chemical properties

Leucine is a branched-chain amino acid
Branched-chain amino acids
A branched-chain amino acid is an amino acid having aliphatic side-chains with a branch...

 (BCAA) since it possesses an aliphatic side-chain that is non-linear.

In chemistry, a racemic mixture, or racemate , is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. The first known racemic mixture was "racemic acid", which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid.- Nomenclature :A...

 leucine had been subjected to circularly polarized synchrotron radiation
Synchrotron radiation
The electromagnetic radiation emitted when charged particles are accelerated radially is called synchrotron radiation. It is produced in synchrotrons using bending magnets, undulators and/or wigglers...

 in order to better understand the origin of biomolecular asymmetry. An enantiomeric enhancement of 2.6 % had been induced, indicating a possible photochemical origin of biomolecules' homochirality
Homochirality is a term used to refer to a group of molecules that possess the same sense of chirality. Molecules involved are not necessarily the same compound, but similar groups are arranged in the same way around a central atom. In biology homochirality is found in the chemical building blocks...


Food additive

As a food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

, L-Leucine has E number
E number
E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...

 E641 and is classified as a flavor enhancer.

See also

  • Leucines
    The leucines are primarily the four isomeric amino acids: leucine, isoleucine, tert-leucine and norleucine. Being compared with the four butanols, they could be classified as butyl-substituted glycines; they represent all four possible variations....

    , description of the isomers of leucine
  • Photo-reactive leucine
    Photo-reactive amino acid analog
    Photo-reactive amino acid analogs for in-vivo crosslinking of protein complexes were introduced in 2005 by researchers from the Max Planck Institute. In this method, cells are grown with photoreactive diazirine analogs to leucine and methionine, which are incorporated into proteins...

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