[32] Ergothioneine as antioxidant

Publisher Summary This chapter discusses the role of ergothioneine as antioxidant. One important attribute of ergothioneine is that the standard redox potential at pH 7 of the thiol–disulfide couple of ergothioneine is -0.06 V as opposed to -0.20 to -0.32 V for other widely occurring natural thiols. The disulfide of ergothioneine is reduced by cysteine with the production of cystine. Halogens readily remove the sulfur of ergothioneine, whereas the other thiols are stable. A second important attribute of ergothioneine is its presence in aqueous solutions predominantly as the thione rather than as the thiol; the thiolate ion is present in basic solutions. Because of its redox potential and propensity to tautomerize to the thione, ergothioneine shares only some properties of representative thiols and thiones. A wide array of functions has been proposed for ergothioneine. A primary function of ergothioneine, both in its native species and in organisms assimilating it, is its service as an interceptor of H 2 O 2 , some radical species, and some toxic electrophilic organic molecules. Ergothioneine is oxidized and catalyzes the oxidation of reduced glutathione to the disulfide in the presence of H 2 O 2 . Ergothioneine and catalase protect the germination of ergot conidia from H 2 O 2 ; H 2 O 2 is an agent that may be used by plants as a defense against fungal infection.