Calorimetric evidence for different structural roles of Glu132 and Glu133 residues in human superoxide dismutase

DSC measurements have been performed on human superoxide dismutase (HSOD) and on its mutants on the Glu132 and Glu133 residues which have been alternatively modified to a Gln residue. In both cases, the substitution has dramatic effects on the thermal denaturation of HSOD as evidenced by the calorimetric experiments. In particular, replacement of the Glu residue in position 132 seems to have a greater effect on the stabilization of the protein, highlighting the key role played by this position. All the experimental data are qualitatively explained in terms of interactions between the groups which form the active site channel.