β-Alanine
β-Alanine (beta-alanine) is a naturally occurring beta amino acid, which is an amino acid in which the amino group is attached to the β-carbon atom (i.e. the carbon atom two carbon atoms away from the carboxylate group) instead of the more usual α-carbon atom for alanine (α-alanine). The IUPAC name for β-alanine is 3-aminopropanoic acid. Unlike its counterpart α-alanine, β-alanine has no stereocenter.
Biosynthesis and industrial route
In terms of its biosynthesis, it is formed by the degradation of dihydrouracil and carnosine. β-Alanine ethyl ester is the ethyl ester which hydrolyses within the body to form β-alanine.[1] It is produced industrially by the reaction of ammonia with β-propiolactone.[2]
Sources for β-alanine includes pyrimidine catabolism of cytosine and uracil.
Biochemical function
β-Alanine residues are rare. It is a component of the peptides carnosine and anserine and also of pantothenic acid (vitamin B5), which itself is a component of coenzyme A. β-alanine is metabolized into acetic acid.
Precursor of carnosine
β-Alanine is the rate-limiting precursor of carnosine, which is to say carnosine levels are limited by the amount of available β-alanine, not histidine.[3] Supplementation with β-alanine has been shown to increase the concentration of carnosine in muscles, decrease fatigue in athletes, and increase total muscular work done.[4][5] Simply supplementing with carnosine is not as effective as supplementing with β-alanine alone since carnosine, when taken orally, is broken down during digestion to its components, histidine (which people usually already have enough of from regular protein consumption) and β-alanine. Hence, by weight, only about 40% of the dose is available as β-alanine.[3]
Because β-alanine dipeptides are not incorporated into proteins, they can be stored at relatively high concentrations. Occurring at 17–25 mmol/kg (dry muscle),[6] carnosine (β-alanyl-L-histidine) is an important intramuscular buffer, constituting 10-20% of the total buffering capacity in type I and II muscle fibres. In carnosine, the pKa of the imidazolium group is 6.83, which is ideal for buffering.[7]
Receptors
Even though much weaker than glycine (and, thus, with a debated role as a physiological transmitter), β-alanine is an agonist next in activity to the cognate ligand glycine itself, for strychnine-sensitive inhibitory glycine receptors (GlyRs) (the agonist order: glycine ≫ β-alanine > taurine ≫ alanine, L-serine > proline).[8]
β-alanine has five known receptor sites, including GABA-A, GABA-C a co-agonist site (with glycine) on NMDA receptors, the aforementioned GlyR site, and blockade of GAT protein-mediated glial GABA uptake, making it a putative "small molecule neurotransmitter."[9]
Athletic performance enhancement
There is evidence that β-alanine supplementation can increase exercise and cognitive performance,[10][11][12][13] for some sporting modalities,[14] and exercises within a 0.5–10 min time frame.[15] β-alanine is converted within muscle cells into carnosine, which acts as a buffer for the lactic acid produced during high-intensity exercises, and helps delay the onset of neuromuscular fatigue.[12][16]
Ingestion of β-alanine can cause paraesthesia, reported as a tingling sensation, in a dose-dependent fashion.[13] Aside from this, no important adverse effect of β-alanine has been reported, however, there is also no information on the effects of its long-term usage or its safety in combination with other supplements, and caution on its use has been advised.[10][11] Furthermore, many studies have failed to test for the purity of the supplements used and check for the presence of banned substances.[12]
Metabolism
β-Alanine can undergo a transamination reaction with pyruvate to form malonate-semialdehyde and L-alanine. The malonate semialdehyde can then be converted into malonate via malonate-semialdehyde dehydrogenase. Malonate is then converted into malonyl-CoA and enter fatty acid biosynthesis.[17]
Alternatively, β-alanine can be diverted into pantothenic acid and coenzyme A biosynthesis.[17]
References
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- ↑ Encyclopedia of Life Sciences Amino Acid Neurotransmitters. Jeremy M Henley, 2001 John Wiley & Sons, Ltd. Script error: No such module "CS1 identifiers"., Article Online Posting Date: April 19, 2001
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External links
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