Ophthalmic acid, also known as ophthalmate (chemically L-Ύ-glutamyl-L-α-aminobutyrylglycine), is a tripeptide analogue of glutathione

Glutathione

Glutathione is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain...

 in which the cysteine

Cysteine

Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...

 group is replaced by L-2-aminobutyrate. It was first discovered and isolated from calf lens.

Biosynthesis

Recent studies have shown that the ophthalmate can be biologically synthesized from 2-amino butyric acid through consecutive reactions with gamma-glutamylcysteine synthetase

Gamma-glutamylcysteine synthetase

Gamma-glutamylcysteine synthetase is the first enzyme in the glutathione biosynthesis pathway.-Function:...

 and glutathione synthetase

Glutathione synthetase

Glutathione synthetase is the second enzyme in the glutathione biosynthesis pathway. It catalyses the condensation of gamma-glutamylcysteine and glycine, to form glutathione.In eukaryotes, this is a homodimeric enzyme...

. So the ophthalmic acid could be used as a biomarker in oxidative stress

Oxidative stress

Oxidative stress represents an imbalance between the production and manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage...

where the depletion of glutathione takes place.