May play a role in preventing oxidative stress by metabolizing extracellular oxidized glutathione (GSSG). an alpha-amino acid + an N-terminal (5-L-glutamyl)-[peptide] = 5-L-glutamyl amino acid + N-terminal L-alpha-aminoacyl-[peptide] glutathione + H2O = L-cysteinylglycine + L-glutamate an S-substituted glutathione + H2O = an S-substituted L-cysteinylglycine + L-glutamate Sulfur metabolism; glutathione metabolism. Associated with the plasma membrane and cell wall. Expressed in embryo, roots and leaves. In mature plants, expression is restricted to vascular tissues of roots, leaves, flowers and siliques. By glutathione. Slight reduction in size, early flowering and increased chlorosis in older leaves. Accumulation of GSSG in the apoplastic space. Belongs to the gamma-glutamyltransferase family.