Hydrolysis of nucleoside triphosphates catalyzed by the recA protein of Escherichia coli. Steady state kinetic analysis of ATP hydrolysis.

The DNA-dependent ATPase activity of the recA protein of Escherichia coli shows a complex dependence on ATP concentration. With a single-stranded (SS) DNA cofactor, the Hill coefficient for ATP is 3.3 at pH 8.1 and 1.4 at pH 6.2. With a double-stranded (DS) DNA cofactor, the Hill coefficient is 3.3 at pH 6.2 (no reaction is detectable at pH 8.1). In the presence of SS DNA, the Km for ATP is 20 microM, independent of pH, while with DS DNA at pH 6.2, KmATP is 100 microM. These and other observations indicate that the interaction of recA protein with ATP is influenced by both pH and DNA cofactor. ADP, UTP, dTTP, and GTP are competitive inhibitors of the ATPase activity of recA protein, indicating that there is a single binding site for nucleoside triphosphates. Nucleoside triphosphates, but not ADP, reduce the Hill coefficient for ATP hydrolysis and thus can contribute to the cooperative effect of ATP.