Glutathione metabolism in Escherichia coli

Abstract

Glutathione is the most abundant low-molecular-weight thiol compound in aerobic bacterial cells. Although its biosynthetic pathway in Escherichia coli is known, its degradative pathway is not clear. We have studied its degradative pathway using E. coli K-12 as a model bacterium. Glutathione synthesized during the exponential phase of growth is excreted into the medium. During the stationary phase, extra cellular glutathione penetrates into the periplasm where its γ-glutamyl residue is cleaved off by γ-glutamyltranspeptidase localized in the periplasm. The released cysteinylglycine is taken up into the cytoplasm through peptide transport systems and the peptide linkage of cysteinylglycine is cooperatively cleaved by enzymes with cysteinylglycinase activity. The resultant cysteine and glycine are used as cysteine and glycine sources, respectively. This cycle acts as a salvage system for cysteine (glycine) in the cells. γ-Glutamyltranspeptidase, the key enzyme of this cycle, was studied extensively not only from a physiological point of view, but also with the aim of applying this enzyme as a catalyst for the synthesis of useful γ-glutamyl compounds.