Figure 6.

Dependence of the rate constant for Rieske cluster reoxidation on salicylate or O₂ concentration. (Black) Salicylate was reacted with fully reduced S5HH (38 μM) and O₂ (900 μM). (Red) O₂ was reacted with fully reduced S5HH (50 μM) and salicylate (2 mM). Reactants were mixed using a stopped-flow spectrophotometer in standard buffer at 4 °C and the reaction time course monitored at 453 nm (concentrations after mixing). Rate constants were determined from multiple summed exponential fits to the data at 453 nm (average of 2–5 time courses) and the fastest 1/τ is plotted. The error at each point is approximately ±10 %. Little or no concentration dependence was observed for the reaction monitored at 700 nm.