Activation of Deoxyribonucleases by Divalent Cations

The activation of DNase I by Mg, Mn, Co, Ni, Fe, Cd, Zn, Ba, Sr, Ca, and Cu ions has been studied by several methods, at different pH and salt concentrations. Mg, Mn, and Co are the best activators for initial stages of degradation. A synergistic effect is shown only by the pair Mg-Ca. Optimal pH of action is always situated at 6.5. DNase II is activated to about the same degree by alkaline earths and Mn ions. Cd and Cu are strong inhibitors. Optimal pH is always 4.6. By titration of liberated secondary phosphate groups, two stages in the hydrolysis of DNA by DNase I are evidenced: a rapid phase activated most by Mg and a slow phase activated by Ca. Some possible mechanisms of action of both enzymes are outlined and the general influence of metal ions is discussed.