Abstract: Ergothioneine (EGT), a naturally occurring amino acid with strong antioxidant property, is produced by only a few microorganisms, including Actinobacteria, Cyanobacteria, and some fungi like Streptomyces and Mycobacteria. Although EGT cannot be synthesized in animals (including human) and plants, plants can absorb EGT synthesized by microorganisms from the soil through their roots, while animals can absorb and accumulate dietary EGT. EGT is easily absorbed by the human body via the organic cation transporter 1 (OCTN1) and is widely distributed in human cells and tissues. Numerous studies have elucidated the biosynthesis, distribution, chemical properties, and antioxidant activity of EGT. Despite intensive efforts in investigating its antioxidant and cytoprotective capacity in vitro against a variety of oxidative stresses, its physiological roles and potential mechanisms of action in vivo have not been fully determined yet. This review aims to elucidate the unique properties and biosynthesis of EGT as well as its potential as a therapeutic agent in the prevention of diseases.

Key words: ergothioneine, biosynthesis, antioxidant property, physiological role, application