Multiple conformations of deoxyribonuclease A. Their separation at alkaline pH and low ionic strength in the presence of Ca2+.

Gel filtration on Sephadex G-100 at pH 9.0 in 1 mM Tris buffer produces denaturation and inactivation of pancreatic DNAase A. Limiting concentrations of Ca2+ in the suspension and elution buffer, reactivates some of the enzyme molecules in an amount proportional to the calcium added. Stable active and inactive forms were separated on Sephadex columns. A model for the conformational role of Ca2+ on DNAase A demonstrates that at least one Ca2+ is involved (Kapp = 8.3 . 10(-5) M) in the correct folding of the polypeptide chain. Na+ was unable to reactivate the enzyme.