Kinetic analysis of human EndoG. (A) Electrophoresis analysis. EndoG (0.05 pmol) was mixed with various amounts of supercoiled pUC18 dsDNA and incubated at 37°C for 3 min. The resulting products were then analyzed by 1.2% agarose gels. Arrowheads denote the different topological forms of pUC18 plasmids. OC: open circular; L: linear; SC: supercoiled. (B) Initial velocity of DNA cleavage as a function of substrate concentration. Steady-state kinetic parameters were determined by curve fitting of these values to the Michaelis-Menten equation.