Figure 4.
Computer simulation of SO dismutation with different [catalyst]. The time courses of SO optical signal were simulated using SCoP based on a kinetic model including parallel irreversible self-dismutation (eq 1) and catalyzed dismutation (eq 2 and 3). The SO self-dismutation rate constant was set at measured value at pH 8.5, ks = 3.3 × 104 M−1s−1 (Figure 1); the rate constants of catalyzed SO dismutation were set at identical kr = ko; [SO] was set at 100 μM and [catalyst] varied from 20 nM to 20 μM. The time course of self-dismutation is represented by black circles and those of catalyzed reactions by solid lines. The [catalyst] used in simulations are marked in each panel: 20 nM (A) & (F); 100 nM (B); 500 nM (C); 2 μM (D); 20 μM (E).The varying rate constants used in each panel: 1 × 105 M−1s−1, black; 1 × 106 M−1s−1, red; 1 × 107 M−1s−1, green;1 × 108 M−1s−1, yellow; 1 × 109 M−1s−1, blue. Panel F: biphasic exponential fits to the simulated time courses (same as in (A) represented with open circles) using the same color scheme as above. The fit rate constants are divided by [catalyst] = 20 nM to obtain the 2nd-order rate constants: 3.7 × 108/9.0 × 107 M−1s−1 (black); 3.7 × 108/9.0 × 107 M−1s−1 (red); 3.8 × 108/9.2 × 107 M−1s−1 (green); 4.8 × 108/1.4 × 108 M−1s−1 (yellow); 2.2 × 109/9.8 × 108 M−1s−1 (blue).