(A) Concentration of resorufin plotted as a function of time (symbols) in steps of 0.1 s obtained from transmission measurements (at λmax=571 nm). The solution contains 280±6 μm AR, 5.5±0.1 nm HRP, and either 3.8±0.1 μm, 7.8±0.1 μm, or 15.5±0.3 μm H2 O2. The transmission spectrum, along with Eq. (5), was used to find the concentration of resorufin. The measurements were repeated three times at each [H2 O2] value; the data in the figure shows the average value. Experimental data points are reported every 5 s for clarity; the confidence band indicates the error for all data points. The fits (solid lines) are obtained using a pseudo-first-order kinetics model (Eqs. 4C–4F) with K1=0 and K3=56±7 m-1 s-1 as previously determined from , Appendix D. (B) The average rate constant K2 was determined for three independent trials at each concentration of H2 O2 (the error bars are within the data points). The mean value of all trials and concentrations is K2=135±5 m-1 s-1.