On the mechanism of metal activation of deoxyribonuclease I

Abstract

1. 1. The activation of deoxyribonucleasc I (DNase I) by Mg ++, Mn ++, and Ca ++ has been studied at 27 °C., at an ionic strength of 0.15, and at a pH of 7.5 - 7.2. Alone, the metals rank us activators in the order Mn ++ > Mg ++ ⪢ Ca ++. 2. 2. Activity in the presence of Mg ++ or Mn ++ has been shown to require the formation of a “metallosubstrate.” 3. 3. In a study of activation by pairs of these metals, Ca ++ was found to be a potent Synergist in the Mg-activated reaction, increasing the maximum rate more than threefold, to give a rate comparable to that given by Mn ++ alone. Several possible explanations are suggested. 4. 4. A rapid method is described for standardizing solutions of a large number of bivalent metal salts. 5. 5. Several pitfalls in DNase I assay methods are discussed and modifications suggested. 6. 6. The inhibition of DNase I by citrate has been studied and is to be deprecated; ethylenediaminetetraacetic acid is suggested to replace citrate. 7. 7. The dissociation constant of Mn citrate was determined to be 1.90 ± 0.13 × 10 −4, using an ion-exchange radioisotope method.