Leucine

Leucine

Names
IUPAC name Leucine
Other names 2-Amino-4-methylpentanoic acid
Identifiers
CAS Number	61-90-5 Y
ChEBI	CHEBI:57427 Y
ChEMBL	ChEMBL291962 N
ChemSpider	5880 Y
DrugBank	DB01746 Y
IUPHAR/BPS	3312
Jmol 3D model	Interactive image
KEGG	D00030 Y
PubChem	6106
UNII	GMW67QNF9C Y
InChI InChI=1S/C6H13NO2/c1-4(2)3-5(7)6(8)9/h4-5H,3,7H2,1-2H3,(H,8,9)/t5-/m0/s1 Y Key: ROHFNLRQFUQHCH-YFKPBYRVSA-N Y InChI=1/C6H13NO2/c1-4(2)3-5(7)6(8)9/h4-5H,3,7H2,1-2H3,(H,8,9)/t5-/m0/s1 Key: ROHFNLRQFUQHCH-YFKPBYRVBU
SMILES CC(C)C[C@@H](C(=O)O)N
Properties
Chemical formula	C6H13NO2
Molar mass	131.18 g·mol−1
Acidity (pKa)	2.36 (carboxyl), 9.60 (amino)
Vapor pressure	{{{value}}}
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
N verify (what is YN ?)
Infobox references

Leucine (abbreviated as Leu or L; encoded by the six codons UUA, UUG, CUU, CUC, CUA, and CUG) is an ɑ-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated -+NH3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated –COO- form under biological conditions), and an isobutyl side chain, classifying it as a nonpolar (at physiological pH) amino acid. It is essential in humans, meaning the body cannot synthesize it and thus it must be obtained from the diet.

Leucine is a major component of the subunits in ferritin, astacin, and other "buffer" proteins.

Biology

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.

Biosynthesis

As an essential amino acid, leucine cannot be synthesized by animals. Consequently, it must be ingested, usually as a component of proteins. In plants and microorganisms, leucine is synthesised from pyruvic acid by a series of enzymes:

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

Synthesis of the small, hydrophobic amino acid valine also includes the initial part of this pathway.

Effects

Leucine is an activator of mTOR; it is the only dietary amino acid that has the capacity to directly 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. However, results of comparative studies are conflicted. Long-term leucine supplementation does not increase muscle mass or strength in healthy elderly men. More studies are needed, preferably those which utilize an objective, random sample of society. Factors such as lifestyle choices, age, gender, diet, exercise, etc. must be factored into the analyses in order to isolate the effects of supplemental leucine as a standalone, or if taken with other branched chain amino acids (BCAAs). Until then, dietary supplemental leucine cannot be associated as the prime reason for muscular growth or optimal maintenance for the entire population.

Leucine potently activates the mammalian target of rapamycin kinase that regulates cell growth. Infusion of leucine into the rat brain has been shown to decrease food intake and body weight via activation of the mTOR pathway.

Both L-leucine and D-leucine protect mice against seizures. D-leucine also terminates seizures in mice after the onset of seizure activity, at least as effectively as diazepam and without sedative effects.

Safety

Leucine toxicity, as seen in decompensated maple syrup urine disease (MSUD), causes delirium and neurologic compromise, and can be life-threatening.

Excess leucine may be a cause of pellagra, whose main symptoms are "the four D's": diarrhea, dermatitis, dementia and death, though the relationship is unclear.

Leucine at a dose exceeding 500 mg/kg/d was observed with hyperammonemia. As such, the UL for leucine in healthy adult men can be suggested at 500 mg/kg/d or 35 g/d under acute dietary conditions.

Dietary sources

Food sources of leucine

Food	g/100g
Soybeans, mature seeds, raw	2.97
Beef, round, top round, separable lean and fat, trimmed to fat, select, raw	1.76
Peanuts	1.672
Salami, pork	1.63
Fish, salmon, pink, raw	1.62
Wheat germ	1.571
Almonds	1.488
Chicken, broilers or fryers, thigh, meat only, raw	1.48
Chicken egg, yolk, raw, fresh	1.40
Oat	1.284
Beans, pinto, cooked	0.765
Lentils, cooked	0.654
Chickpea, cooked	0.631
Corn, yellow	0.348
Cow milk, whole, 3.25% milk fat	0.27
Rice, brown, medium-grain, cooked	0.191
Milk, human, mature, fluid	0.10

Chemical properties

(S)-Leucine (or L-leucine), left; (R)-leucine (or D-leucine), right, in zwitterionic form at neutral pH

Leucine is a branched-chain amino acid (BCAA) since it possesses an aliphatic side-chain that is non-linear.

Racemic leucine had been subjected to circularly polarized synchrotron radiation 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.

Other uses

As a food additive, L-leucine has E number E641 and is classified as a flavor enhancer.

See also

• Leucines, the isomers and derivatives of leucine

External links

• Leucine biosynthesis
• 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
• A leucine-supplemented diet restores the defective postprandial inhibition of proteasome-dependent proteolysis in aged rat skeletal muscle