Acidic peptides of the lens. 4. The biosynthesis of ophthalmic acid

Abstract

Lens extracts catalyze the synthesis of the tripeptide, ophthalmic acid, from its constituent amino acids and adenosine triphosphate. The synthesis proceeds through the intermediate formation of gamma-glutamyl-[alpha]-amino-[eta]-butyric acid. Either (or both) of the enzymes of glutathione synthesis are also involved in the synthesis of ophthalmic acid. Analogous tripeptides are synthesized when [alpha] -amino-[eta]-butyric acid is replaced by alanine or threonine. Liver extracts catalyze the hydrolysis of ophthalmic acid to its three amino acids. Rabbit lens extracts contain little, it any, ophthalmic acid, but catalyze its synthesis just as effectively as do calf lens extracts.