β-Alanine (or beta-alanine) is a naturally occurring beta amino acid, which is an amino acid in which the amino group is at the β-position from the carboxylate group (i.e., two atoms away, see Figure 1). The IUPAC name for β-alanine is 3-aminopropanoic acid. Unlike its counterpart α-alanine, β-alanine has no stereocenter.
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. 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. 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 and β-alanine. Hence, by weight, only about 40% of the dose is available as β-alanine.
Figure 1: Comparison of β-alanine (right) with the more customary (chiral) amino acid, L-α-alanine (left)
L-Histidine, with a pKa of 6.1 is a relatively weak buffer over the physiological intramuscular pH range. However, when bound to other amino acids, this increases nearer to 6.8-7.0. In particular, when bound to β-alanine, the pKa value is 6.83, making this a very efficient intramuscular buffer. Furthermore, because of the position of the beta amino group, β-alanine dipeptides are not incorporated into proteins, and thus can be stored at relatively high concentrations (millimolar). Occurring at 17–25 mmol/kg (dry muscle), 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.
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).
Athletic performance enhancement
There is evidence that β-alanine supplementation can increase exercise and cognitive performance, but there is concern about lack of information about safety.
Ingestion of β-Alanine can cause paraesthesia, reported as a tingling sensation, in a dose-dependent fashion.
Sources for β-alanine includes pyrimidine catabolism of cytosine and uracil.
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