Effect of monovalent cations on the activity of the DNA polymerase of Escherichia coli B.

Abstract

The effect of a number of inorganic salts containing monovalent cations on the activity of the DNA polymerase from E. coli B has been investigated under a variety of conditions. The following results were obtained. In the presence of buffers prepared from organic amines and HCl the enzyme activity is stimulated 3‐ to 15‐fold by chlorides containing K+, Rb+, Cs+ or NH+4. The buffer concentration influenced the degree of stimulation and the shape of the activation curves. The activation constant for KCl decreased with increasing buffer concentration and with increasing pH. NaCl and LiCl had little or no stimulating effect. The latter two salts counteracted the stimulating effect of the four former salts. In the absence of amine‐HCl buffers it was found that below certain concentrations sodium, potassium and lithium glycinate buffers and potassium and sodium phosphate buffers stimulated the enzyme activity. Data were obtained in favour of the possibility that the monovalent cations under these conditions are indispensible activators for the DNA polymerase reaction. The pattern of stimulation of the enzyme activity by KCl at various amine‐HCl buffer concentrations was similar at different pH values in the pH range from 6.5 to 9.3. At pH 10.5, however, KCl stimulated at low buffer concentrations while all concentrations of this salt inhibited at higher buffer concentrations. In the presence of optimal concentrations of KCl and amine‐HCl buffers the pH optimum curve had a plateau reaching from pH 7.7 to about pH 10.5. The stimulating effect on the enzyme activity observed for potassium salts seems not to be due to an effect on the binding of the substrates to the enzyme but rather to an effect on the catalytic activity of the enzyme. The DNA degrading activity of the enzyme preparation was stimulated by KCl and inhibited by LiCl.