The Interaction of Metal Ions with Polynucleotides and Related Compounds

The activity of ribonuclease increases with increasing concentration of added divalent metal ions until the attainment of an optimal metal concentration, beyond which the addition of further metal ions inhibits the reaction. When either the optimal metal concentration or the enzymatic activity at that concentration is plotted versus the atomic number of the transition metals, the resulting curves can be correlated with the stability constants of complexes of the metals. These results are in line with metal ions reacting at two types of sites, one activating and the other inhibiting. Crystalline bovine pancreatic ribonuclease is affected in the same way as ribonuclease A. The activation of deoxyribonuclease I has been reinvestigated. Metal ions generally activate this enzyme, but the relative activating ability of the various metal ions is not readily correlated with complexing ability, as in the case of ribonuclease. Co(II) activates deoxyribonuclease I better than the metals that have generally been used for this purpose.