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Structural formula
L-Leucine - L-Leucine.svg
Structure of L- leucine, the naturally occurring isomer
Surname Leucine
other names
Molecular formula C 6 H 13 NO 2
Brief description

shimmering white crystal scales

External identifiers / databases
CAS number
  • 61-90-5 ( L -enantiomer)
  • 328-38-1 ( D -enantiomer)
  • 328-39-2 ( racemate )
EC number 200-522-0
ECHA InfoCard 100,000,475
PubChem 6106
ChemSpider 5880
DrugBank DB00149
Wikidata Q483745
Drug information
ATC code


Molar mass 131.18 g mol −1
Physical state



1.29 g cm −3

Melting point

293-295 ° C

pK s value
  • pK COOH : 2.33
  • pK NH 3 + : 9.74
safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Leucine , abbreviated to Leu or L , is a proteinogenic α - amino acid . It crystallizes in white platelets, from which the name is derived ( Gr. Λευκός: white).

Leucine belongs together with its structural isomers isoleucine , norleucine and tert -leucine to the substance group of Leucine .


For higher living beings, L- leucine [synonym: ( S ) -leucine] is an essential amino acid that probably plays a central role in the energy balance in muscle tissue. The mirror image isomer (synonym: enantiomer) of L- leucine is D- leucine [synonym: ( R ) -leucine]. The latter does not occur in proteins.

In this text, the information on physiology only relates to L- leucine [synonym: ( S ) -leucine]. Whenever “leucine” is mentioned in this article and in the scientific literature without any addition, it always means L- leucine . Racemic DL -Leucine [Synonym: ( RS ) -Leucine] and enantiomerically pure D -Leucine [Synonym: ( R ) -Leucine] are synthetically accessible and are of little practical importance. The racemization of L- amino acids can be used for amino acid dating - an age determination for fossil bone material.

L- leucine is encoded by the codons UUA, UUG, CUU, CUC, CUA and CUG.

Isomers of leucine
Surname L- leucine D -Leucine
other names ( S ) -Leucine ( R ) -Leucine
Structural formula L-Leucine - L-Leucine.svg D-Leucine.svg
CAS number 61-90-5 328-38-1
328-39-2 (racemate)
EC number 200-522-0 206-327-7
206-328-2 (racemate)
ECHA info card 100,000,475 100.005.753
100.005.754 (racemate)
PubChem 6106 439524
- (racemate)
DrugBank DB00149 DB01746
- (racemate)
Wikidata Q483745 Q16081973
Q60662890 (racemate)


In 1819 the French pharmacist and chemist Joseph Louis Proust was able to isolate two substances from wheat flour, which he called "acid caséique" and "oxide caséeux". A year later, Henri Braconnot isolated a seemingly new substance from muscle fiber and wool by acid hydrolysis and named it leucine because of the white color of the crystals. Eduard Mulder recognized the identity of the two substances in 1839 and discussed their possible composition. But it was not until 1891 that the German chemist Ernst Schulze and his doctoral student Arthur Likiernik succeeded in correctly determining the constitution of L- leucine.


Leucine is - bound in peptides - a component of animal and vegetable protein. The following examples each relate to 100 g of the food; the percentage of leucine in the total protein is also given:

Food Total protein Leucine proportion of
Beef, raw 21.26 g 1691 mg 0 8.0%
Chicken breast fillet, raw 23.09 g 1732 mg 0 7.5%
Salmon, raw 20.42 g 1615 mg 0 7.9%
Chicken egg 12.58 g 1088 mg 0 8.6%
Cow's milk, 3.7% fat 0 3.28 g 0 321 mg 0 9.8%
Walnuts 15.23 g 1170 mg 0 7.7%
Wholemeal wheat flour 13.70 g 0 926 mg 0 6.8%
Wholemeal corn flour 0 6.93 g 0 850 mg 12.3%
Rice, unpeeled 0 7.94 g 0 657 mg 0 8.3%
Peas, dried 24.55 g 1760 mg 0 7.2%


Leucine is mainly present as an “inner salt” or zwitterion , the formation of which can be explained by the fact that the proton of the carboxy group migrates to the lone pair of electrons on the nitrogen atom of the amino group .

Zwitterions of L- leucine (left) or D- leucine (right)

The zwitterion does not migrate in the electric field because it is uncharged as a whole. Strictly speaking, this is the case at the isoelectric point (at a certain pH value), at which the leucine also has its lowest solubility in water. The isoelectric point is 5.98. Racemic leucine, which was exposed to circularly polarized synchrotron radiation for a better understanding of homochirality in the biosphere , shows an enantiomeric excess of 2.6%.


L- leucine is important for maintaining and building muscle tissue. It supports protein synthesis in muscles and liver, inhibits the breakdown of muscle protein and supports healing processes. Like L - isoleucine , L- leucine can also serve as an energy supplier.

Estimates of the daily requirement for healthy adults range, depending on the method used, from 10 to 50 mg of leucine per kilogram of body weight. A deficiency is caused either by inadequate intake with food or insufficient supply of vitamin B6 .


L- leucine, along with glycine and other proteinogenic L- amino acids, is a component of medical infusion solutions.

In weight training , leucine is used as a dietary supplement to build muscle.

See also


  • Hans Beyer and Wolfgang Walter : Textbook of Organic Chemistry , 20th Edition, S. Hirzel Verlag, Stuttgart, 1984, ISBN 3-7776-0406-2 .
  • Hans-Dieter Jakubke and Hans Jeschkeit: Amino acids, peptides, proteins , Verlag Chemie, Weinheim, 1982, ISBN 3-527-25892-2 .
  • Jesse Philip Greenstein and Milton Winitz: Chemistry of Amino Acids , John Wiley & Sons, 1962, Volumes 1 to 3, ISBN 0-471-32637-2 .
  • Yoshiharu Izumi, Ichiro Chibata and Tamio Itoh: Production and Utilization of Amino Acids , In: Angewandte Chemie International Edition in English , 1978, 17 , pp. 176-183.

Web links

Commons : Leucine  - Collection of images, videos and audio files

Individual evidence

  1. Entry on E 641: L-leucine in the European database for food additives, accessed on August 6, 2020.
  2. entry to LEUCINE in CosIng database of the European Commission, called on August 6, 2020th
  3. a b c d Entry on l-leucine. In: Römpp Online . Georg Thieme Verlag, accessed on December 25, 2014.
  4. a b Leucine data sheet (PDF) from Carl Roth , accessed on December 18, 2012.
  5. ^ A b Hans Beyer and Wolfgang Walter: Textbook of Organic Chemistry , S. Hirzel Verlag, Stuttgart 1991, ISBN 3-7776-0485-2 , p. 823.
  6. Hans-Dieter Jakubke, Hans Jeschkeit: amino acids, peptides, proteins , Verlag Chemie, Weinheim, 62, 1982, ISBN 3-527-25892-2 .
  7. ^ LJ Proust: Sur le Principe qui assaisonne les Fromages. , Ann Chim Phys, Volume 10, pp. 29ff (1819).
  8. H. Braconnot: Memoire sur un Principe particulier aux graines de la famillie des légumineuses, et analyze des pois et des haricots. Ann Chim Phys, Volume 34, pp. 68ff (1820).
  9. Sabine Hansen: The discovery of proteinogenic amino acids from 1805 in Paris to 1935 in Illinois. ( Memento from June 15, 2016 in the Internet Archive ) Berlin 2015.
  10. E. Schulze, A. Likernik: About the constitution of leucine. Ber Deutsche Chem Ges, Volume 24, pp. 669ff (1891).
  11. nutrient database of the US Department of Agriculture , 21st edition.
  12. PM Hardy: The Protein Amino Acids in GC Barrett (editor): Chemistry and Biochemistry of the Amino Acids , Chapman and Hall, 1985, ISBN 0-412-23410-6 , p. 9.
  13. Meierhenrich : Amino acids and the asymmetry of life , Springer-Verlag, 2008, ISBN 978-3-540-76885-2 .
  14. AV Kurpad, MM Regan, T. Raj, JV Gnanou: Branched-chain amino acid requirements in healthy adult human subjects , in: J. Nutr. , 2006, 136 (1 Suppl) , pp. 256S-263S; PMID 16365094 .