Pre-Steady-State Analysis of ATP Hydrolysis by Saccharomyces cerevisiae DNA Topoisomerase II. 1. A DNA-Dependent Burst in ATP Hydrolysis

When bound to DNA, topoisomerase II from Saccharomyces cerevisiae exhibits burst kinetics with respect to ATP hydrolysis. Pre-steady-state analysis shows that the enzyme binds and hydrolyzes two ATP per reaction cycle. Our data indicate that at least one of the two ATP is rapidly hydrolyzed prior to the rate-determining step in the reaction mechanism. When DNA is not bound to topoisomerase II, the rate-determining step shifts to become either ATP binding or hydrolysis. Two possible mechanisms are proposed that agree with our observations.