Differential pH sensitivity of tissue superoxide dismutases

Superoxide dismutase (SOD) activities in the human and rat RBCs and rat liver, kidney, brain and heart mitochondria as well as cytosolic fractions were determined by the pyrogallol assay procedure with slight modifications. Measurements were carried out in 0.1 M potassium phosphate buffer pH 8.0 and 9.2 to assess the pH stability of the SODs from various systems. Under these conditions the SODs from different systems including RBCs exhibited differential pH stability i.e. they displayed differential susceptibility at pH 9.2. Even in a given tissue, the mitochondrial and cytosolic SODs contents show a tissue-specific pattern. Our results also suggest that measurements carried out at pH 8.0 may give more realistic estimates of SOD activities.