Glutathione transferases (GSTs) are an important class of enzymes involved in cellular detoxification.GSTs are found in all classes of organisms and are implicated in resistance towards drugs, pesticides, herbicides and antibiotics.The activity, structure and folding, particularly of eukaryotic GSTs, has therefore been widely studied.The crystal structure of GST from Escherichia coli(EGST) was reported around 10 years ago, suggesting Cys 10 and His 106 as potential catalytic residues.However, the role of these residues in catalysis has not been further investigated, nor have the folding properties of the protein been described.In this study, we investigate the contributions of residues Cys 10 and His 106 to the activity and stability of EGST.We found that EGST shows a complex equilibrium unfolding profile, involving population of at least 2 partially-folded intermediates, one of which is dimeric.Mutation of residues Cys10 and His106 leads to stabilization of the protein and affects the apparent steady-state kinetic parameters for enzyme catalysis.The results suggest that the aromatic ring of His 106 plays an important role in the catalytic mechanism of the enzyme, while Cys 10 is involved in binding of the substrate GSH.This study demonstrates that protein engineering of the Cys10 site can increase both the stability and activity of EGST.