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. 2009 Mar 4;106(12):4659–4664. doi: 10.1073/pnas.0804943106

Fig. 3.

Fig. 3.

The O2 dependence and rate of the FNR-S24F [4Fe-4S]2+ cluster conversion upon addition of O2. (A) Reaction of ≈20 μM FNR-S24F with different concentrations of O2 (0, 20, 40, 60, 80, 100, and 150 μM) measured by optical absorbance at 420 nm. Data are shown in gray, and double-exponential function fits are plotted as black lines. Data are the average of at least three experiments. (B) First observed (pseudo-first-order) rate constants, from A, as a function of O2 concentration. (C) Changes in EPR spectra of 20.4 μM FNR-S24F cluster during reaction with 200 μM O2. The reaction was performed in a sealed anaerobic cuvette and initiated by the injection of air-saturated buffer. Samples were transferred to EPR tubes and immediately frozen. EPR parameters: temperature, 15 K; microwave power, 2.0 mW; frequency, 9.7 GHz; modulation, 5 G. (D) Signal intensity of the [3Fe-4S]+ intermediate (expressed as a percentage of the original [4Fe-4S]2+ cluster concentration) as a function of time for FNR (gray bars) and the FNR-S24F mutant protein (black bars).