|Structural formula of L -alanine, the naturally occurring enantiomer|
|Molecular formula||C 3 H 7 NO 2|
|External identifiers / databases|
|Molar mass||89,10 g · mol -1|
1.40 g cm −3
297 ° C (decomposition)
|pK s value||
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
Alanine is chiral , so it occurs in two mirror-image forms, whereby L -alanine is a proteinogenic amino acid which, according to IUPAC, is also referred to as ( S ) -2-aminopropanoic acid or ( S ) -alanine. D- alanine [synonym: ( R ) -alanine] is found as a building block of murein , the basic substance of bacterial cell walls. There is also the non-proteinogenic β-alanine .
Whenever "alanine" is mentioned in this text or in the scientific literature without any additional name ( prefix ), L -alanine is meant.
|Enantiomers of alanine|
|Surname||L -alanine||D -alanine|
|other names||( S ) -alanine||( R ) -alanine|
|ECHA info card||100,000,249||100.005.835|
In addition to proline , alanine is one of the two amino acids that were first synthesized and not previously isolated from plant or animal material. Alanine was found by Adolph Strecker in 1850 when he actually wanted to synthesize lactic acid by reacting acetaldehyde with ammonia and hydrocyanic acid in the presence of hydrochloric acid , using the Strecker synthesis named after him. Strecker chose the name as a derivation of the term aldehyde , since he received the amino acid from the acetaldehyde mentioned. Alanine was first obtained from organic material in 1875 by Paul Schützenberger , when he split silk in an autoclave using barite and was able to identify a mixture of glycine and alanine. Of the amino acids involved in building the protein chain, L- alanine represents 29.7%.
The industrial production of L -alanine is based on L - aspartic acid by splitting off the β - carboxy group in a biotechnological process. Racemic alanine obtained by the Strecker synthesis can be acetylated at the amino group and is then subjected to a racemate resolution . Using L - aminoacylase, the acetyl group of L - N- acetylalanine is cleaved enantioselectively and L -alanine is formed , while D - N -acetylalanine is not hydrolyzed. The separation of L -alanine and D - N -acetylalanine is easy. If D -alanine is required , D - N -acetylalanine is hydrolyzed under acidic conditions, i. i.e., the acetyl group is split off. If there is no need for D -alanine is that obtained in the kinetic resolution is D - N -Acetylalanin by the action of acetic anhydride is racemized and recycled.
DL -Alanine can also be synthesized from 2-bromopropanoic acid, but this process is of no industrial importance.
In the metabolism, L -alanine is synthesized from the end product of glycolysis , pyruvate , through transamination . Bacteria obtain the D -alanine they need from L -alanine by means of the enzyme alanine racemase ( EC 188.8.131.52 ).
Alanine is usually 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 :
At a physiological pH of 7.4, a large proportion of the alanine molecules are present as zwitterions. The isoelectric point of alanine is pH 6.1 and alanine reaches its lowest solubility in water, since almost all alanine molecules are present as zwitterions. The solution has the lowest electrical conductivity at this point because zwitterions as a whole are uncharged.
In reverse of this synthesis reaction, it can also be enzymatically broken down to pyruvate again (transamination). The carbon skeleton can be used again via pyruvate to build up glucose ( gluconeogenesis ) or completely broken down via the citric acid cycle to generate energy. The oxidative deamination of L -alanine to pyruvate and ammonia, catalyzed by the enzyme alanine dehydrogenase, represents a further degradation possibility; it exemplifies how part of the amino acid metabolism is linked to the carbohydrate metabolism .
L -alanine is a non-essential amino acid for humans, so it can be produced biosynthetically by the human metabolism.
Alanine occurs - alongside other amino acids such as B. leucine and glutamic acid - preferred in α-helices of proteins . These amino acids promote the formation of this secondary structural element and are therefore also referred to as helix formers .
L- alanine is a component of infusion solutions for parenteral nutrition and dietetics.
The two enantiomers of alanine, provided with a protective group , are often used for the synthesis of peptides and proteins . Furthermore, L - or D -alanine are also used as starting material in stereoselective synthesis .
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