Pyroglutamic acid

Pyroglutamic acid (also known as PCA, 5-oxoproline, pidolic acid, or pyroglutamate for its basic form) 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. 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, also known as pidolic acid, exists as two distinct enantiomers:
(2R) or D which happens to be (+) or d
(2S) or L which happens to be (–) or l

This page uses material from the related Wikipedia article which is released under the Creative Commons Attribution-Share-Alike License 3.0.