Pyroglutamic acid

Pyroglutamic acid (also known as 5-oxoproline, pidolic acid, or pyroglutamate for its basic form) is an uncommon amino acid derivative in which the free amino group of glutamic acid or glutamine cyclizes to form a lactam. It is found in many proteins including bacteriorhodopsin. N-terminal glutamic acid and glutamine residues can spontaneously cyclize to become pyroglutamate. This is one of several forms of blocked N-terminals 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 is also known as pidolic acid, exists as two distinct enantiomers:
 * (2R) or (+) or l or D
 * (2S) or (–) or d or L

Uses
The sodium salt of pyroglutamic acid – known either as sodium pyroglutamate or sodium pidolate – is used on the skin to retain moisture.

Pyroglutamic acid is sold as a dietary supplement in the United States.