Figure 7.

KpFeoC also binds an redox-active, oxygen-sensitive [4Fe-4S] cluster. A. Absorption spectrum of the cleaved, anaerobically reconstituted KpFeoC protein. Conditions were the same is in Figure 3C. B. Fe EXAFS and Fourier transforms of anaerobically reconstituted KpFeoC. Conditions were the same as in Figure 4B. C. CW X-band EPR spectrum of cleaved and anaerobically-reconstituted KpFeoC reduced with sodium dithionite. Sample conditions were the same as in Figure 5D. Data collection parameters were as follows: 10 K, modulation amplitude 0.5 mT, modulation frequency = 100 kHz, 1024 points, conversion time = 58.59 ms, microwave power = 0.47 mW, 16 scans. A cavity contaminant marked by an asterisk (*) at ≈ 335 mT (g ≈ 2.005) was observed even after background subtraction in all spectra. D. Representative time course spectra of cleaved, anaerobically reconstituted KpFeoC reacting with air-saturated buffer. Spectra were taken every 6 s (black, dotted) immediately after buffer mixing until reactivity stopped. The [4Fe-4S]²⁺ spectral features (goldenrod) are rapidly lost and the appearance of the [2Fe-2S]²⁺ spectral features rapidly appear (purple). The inset represents the plot of the kinetic decay of the absorbance feature at 400 nm (closed circles), characteristic of the [4Fe-4S]²⁺ cluster, and its fitted simulation (black dashed line), revealing a k_obs of (0.030 ± 0.020) s⁻¹ and a t_½ of (34 ± 15) s when averaged over three replicates