Figure 8 (A) Concentration of resorufin plotted as a function of time (symbols) in steps of 0.1 s obtained from transmission measurements (at *λ*_{max}=571 nm). The solution contains 280±6 μ*m* AR, 5.5±0.1 n*m* HRP, and either 3.8±0.1 μ*m*, 7.8±0.1 μ*m*, or 15.5±0.3 μ*m* H_{2} O_{2}. The transmission spectrum, along with Eq. (5), was used to find the concentration of resorufin. The measurements were repeated three times at each [H_{2} O_{2}] 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 *K*_{1}=0 and *K*_{3}=56±7 *m*^{-1} s^{-1} as previously determined from , Appendix D. (B) The average rate constant *K*_{2} was determined for three independent trials at each concentration of H_{2} O_{2} (the error bars are within the data points). The mean value of all trials and concentrations is *K*_{2}=135±5 *m*^{-1} s^{-1}.