Cadmium, chromium, and manganese replacement for iron in iron-superoxide dismutase from Pseudomonas ovalis

The Cd-, Cr-, and Mn-substituted enzymes of iron-superoxide dismutase from Pseudomonas ovalis were prepared from the apoenzyme by using the alkaline treatment method described before (1) with a slight modification. The Cd-substituted enzyme had 1.16 g atoms of Cd per mol of enzyme and no visible absorption. The Cr-substituted enzyme had 1.27 g atoms of Cr per mol of enzyme and had absorption maxima at 530 nm and 670 nm with a shoulder around 370 nm. The Mn-substituted enzyme had 1.27 g atoms of Mn per mol of enzyme and had absorption shoulders around 470 nm and 600 nm. The Cd-, Cr-, and Mn-substituted enzymes had no enzymatic activity. The reactivity of the four sulfhydryl groups and circular dichroism spectra of the Cd-, Cr-, and Mn-substituted enzymes were similar to those of the Fe-reconstituted enzyme. These results indicate that these metals may bind to the same site as Fe in the enzyme. The fluorescence emission intensities of the Cd-, Cr-, and Mn-substituted enzymes were 0.75, 0.46, and 0.69 times that of the apoenzyme, respectively.