Comparative studies on the cell surface DNase and the extracellular DNase of Streptococcus sanguis I

Abstract

DNase fractions, designated here Fr. I and Fr. Ⅱ were isolated by the lysozyme digestion and Brij 58 treatment from aerobically cultured Streptococcus sanguis I.

Optimal pH value of both enzymes was 8.5 and metal ions such as Mg²⁺, Mn²⁺, Ca²⁺, Cu²⁺ did not have any effect on their activity.

On the other hand, the extracellular DNase activated by the addition of Mg²⁺ or Mn²⁺ but was inhibited by Ca²⁺ or Cu²⁺. DNase activity was inactivated especially with high concentration Cu ion (0.1mo1/ml).

Molecular weight of these DNases was determined hy SDS-PAGE. Fr. I was about 85,000~90,000 daltons and Fr. Ⅱ about 40,000~45,000 daltons. Molecular weight of the extracellular DNase was different from that of cell surface DNase. On 0.8% agarose gel electrophoresis both Fr. I and Fr. Ⅱ hydrolyzed native thymus DNA, lamda DNA, fd DNA, and thermally denatured thymus DNA. The specific activity of Fr. I was higher than that of Fr. Ⅱ when the substrate was native thymus DNA, while in another substrate it was smaller in Fr. I than in Fr. Ⅱ.

From these results it can be concluded that the cell surface DNases have poor uniqueness on enzymatic activity, while the extracellular DNase has special activity that the enzyme hydrolyzed native thymus DNA only. There were differences in the DNase activity between Fr. I and Fr. Ⅱ.