Effects of metal ions on mutants of PDE3A.

Each enzyme was dialyzed against metal-free buffer, and the activity was measured and compared with the activity before dialysis after adding each cation at 10 μmol/L, 100 μmol/L, and 1 mmol/L, as indicated on the abscissa. Each mutant is represented by a bar, as indicated in the figures: (upper panel) MgCl₂; (middle panel) CoCl₂; (lower panel) MnCl₂. The activity of PDE3A before dialysis is 100%.