In search of a physiological function for L-ergothioneine

Since its discovery at the turn of the century, attempts to define a physiological function for L-ergothioneine have been unsuccessful. This paper suggests several possible functions for this enigmatic compound or its metabolites. These include: transport of cations or carbon dioxide, catalysis of carboxylation or decarboxylation reactions, mediation of thyroid or antithyroid function, histaminic or antihistaminic action, and cholinergic or anticholinergic action.