Mutational and proteolytic studies on a flexible loop in glutathione synthetase from Escherichia coli B: the loop and arginine 233 are critical for the catalytic reaction

The flexible loop of glutathione synthetase in Escherichia coli B was studied through limited proteolysis and kinetic measurements for the wild type and mutant enzymes. Protein fragmentation and enzyme inactivation was seen as the peptide bond on position arginine 233 and glycine 234of the enzyme was disrupted. Stability of the loop is provided by the presence of substrates in the presence of proteases which is more evident in the wild-type enzyme although glycine did not show any protective effects. The findings suggest the role of the loop as binding site for substrate and its protective function for enzyme stability and activity.