Figure 2.

Dependence of the initial cleavage rate, d[S]/dt, of the secondary reaction on the concentration of added 5′ arms, [A], such as would be generated by cleavage in the primary reaction. The initial cleavage rates, measured as the concentration of the secondary probe cleaved by the enzyme in one minute (nM⋅min⁻¹), were determined at different concentrations of 5′ arm. The reactions were run with 0.2 μM secondary probe, in the absence (●) or presence (○) of 0.4 μM primary probe, to measure the contribution of the primary probe to the background. The slopes of the lines give the cycling cleavage rate of the secondary reaction, α₂, and the intercepts of the y axis indicate the contribution of background, k_b, to the total rate. Error bars indicate the standard deviations obtained from the quadruplicate measurements with each sample.