Pidolic acid

Pidolic acid is an endogenous amino acid derivative where the free amino group of glutamic acid or glutamine cyclizes to generate a lactam. Subsequently it is also a metabolite in the glutathione cycle that is converted to glutamate by the enzyme 5-oxoprolinase. Moreover, N-terminal glutamic acid and glutamine residues can either spontaneously cyclize to become pidolic acid, or be enzymatically transformed by glutaminyl cyclases. In particular, this is ultimately a form of N-termini that is a challenge for N-terminal sequencing using Edman chemistry, which necessitates a free primary amino group that is not present in pidolic acid. Pyroglutamate aminopeptidase can restore a free N-terminus by cleaving off the pyroglutamate residue, however.

Additionally, pidolic acid and certain pidolic acid salts like calcium, magnesium, and potassium pidolic acid are sometimes used as skin or hair conditioning agents because of their humectant effects. In such humectant formulations, hydrophilic amine, hydroxyl, or even carboxyl groups possess high affinities for forming hydrogen bonds with molecules of water, allowing the hygroscopic formulations to attract and retain moisture in the air nearby through absorption, therefore drawing the water vapor into the formulation.