|Preferred IUPAC name
|Systematic IUPAC name
3D model (JSmol)
|Molar mass||g·mol−1 129.115|
|Melting point||184 °C (363 °F; 457 K)|
|Acidity (pKa)||-1.76, 3.48, 12.76|
|Basicity (pKb)||15.76, 10.52, 1.24|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Pyroglutamic acid (also known as PCA, 5-oxoproline, pidolic acid) is a ubiquitous but little studied natural amino acid derivative in which the free amino group of glutamic acid or glutamine cyclizes to form a lactam. The names of pyroglutamic acid conjugate base, anion, salts, and esters are pyroglutamate, 5-oxoprolinate, or pidolate.
It is a metabolite in the glutathione cycle that is converted to glutamate by 5-oxoprolinase. Pyroglutamate is found in many proteins including bacteriorhodopsin. N-terminal glutamic acid and glutamine residues can spontaneously cyclize to become pyroglutamate, or enzymatically converted by glutaminyl cyclases. This is one of several forms of blocked N-termini which present a problem for N-terminal sequencing using Edman chemistry, which requires a free primary amino group not present in pyroglutamic acid. The enzyme pyroglutamate aminopeptidase can restore a free N-terminus by cleaving off the pyroglutamate residue.
Pyroglutamic acid exists as two distinct enantiomers:
- (2R) or D which happens to be (+) or d
- (2S) or L which happens to be (–) or l
As first discovered in 1882, pyroglutamic acid can be formed by heating glutamic acid at 180 °C, which results in the loss of a molecule of water. In living cells, it is derived from glutathione through the action of an enzyme, γ-glutamyl cyclotransferase. Pyroglutamic acid may function in glutamate storage, and acts to oppose the action of glutamate, including in the brain. It also acts on the brain's cholinergic system; Amyloid β containing pyroglutamic acid is increased in Alzheimer's disease; this may be part of the disease process. Increased levels of pyroglutamic acid in the blood, or 5-oxoprolinuria, can occur following paracetamol overdose, as well as in certain inborn errors of metabolism, causing an acidosis known as high anion gap metabolic acidosis.
The sodium salt of pyroglutamic acid — known either as sodium pyroglutamate, sodium PCA, or sodium pidolate — is used for dry skin and hair products, as it is a humectant. It has low toxicity and is not a skin irritant, but its use in products is limited by a high price.
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