Cation activation of desoxyribonuclease

The activation of desoxyribonuclease on desoxyribonucleate, known to occur with Mg⁺⁺ and Mn⁺⁺, has been shown to occur equally well with Co⁺⁺, to nearly the same extent with Fe⁺⁺, and to a lesser extent with Ca⁺⁺, Ba⁺⁺, Sr⁺⁺, Ni⁺⁺, Cd⁺⁺, and Zn⁺⁺. The conditions under which the optimal activation is revealed vary among these ions. Thus, Mg⁺⁺, Mn⁺⁺, and Co⁺⁺ may show marked activation under conditions in which Fe⁺⁺ is nearly ineffective. Since too high a concentration of an ion may be as ineffective as too little, concentration-activation curves were determined for each ion. Per micromole of nucleic acid phosphorus, the optimal effective amount of each ion in micromoles is as follows: Mg⁺⁺ 3, Mn⁺⁺ 3, Co⁺⁺ 3, Fe⁺⁺ 0.3, Ni⁺⁺ 0.3, Ba⁺⁺ 1.7, Ca⁺⁺ 3, Sr⁺⁺ 3, Zn⁺⁺ 0.3, and Cd⁺⁺ 0.3.The optimum pH for the activation with Mg⁺⁺, Co⁺⁺, and Ca⁺⁺ is about 6.5, that with Fe⁺⁺ is at 5.7, while Mn⁺⁺ shows two optima at pH 6.8 and 8.0.Experiments conducted in Pyrex and in quartz vessels showed the same results, and indicated that there was no activation of desoxy-ribonuclease in the absence of added salts.