Biosynthesis and Metabolism of Glutathione in Plants

Glutathione (GSH) is the tripeptide y-glutamyl-cysteinyl-glycine (Figure 1). It has been identified in all eukaryotic organisms thus far examined and in many prokaryotes. In most it is the major nonprotein thiol. Some plants synthesize both GSH and a homologue, which has the C-tenninal glycine replaced with another amino acid. Examples include many legumes that synthesize in addition to GSH, homoglutathione with the structure y-glutamyl-cysteinyl-s-alanine (1), rice and wheat in the family Poaceae that synthesize a tripeptide with the structure yglutamyl-cysteinyl-serine (2), and maize that synthesizes y-glutamyl-cysteinyl-glutamate (3,4). Many aerobic prokaryotes synthesize GSH or a homologue such as glutathionyl-spermidine (5). By contrast, anaerobic bacteria generally do not synthesize GSH (6).