Modification of proteins by glutathionylation. This reversible post-translational modification involves the formation of a mixed disulphide between a free thiol group on a protein and a molecule of glutathione. This may occur through oxidation of a protein-thiol group in response to ROS, and reaction with GSH as shown in the diagram. Alternatively, oxidized GSSG may react with protein-SH groups (for a review, see ). Deglutathionylation may be catalysed by glutaredoxin (Grx) or thioredoxin (Trx).