Figure 8.

YtfE-derived NO damages Fe-S clusters. (A) CD spectrum of a deoxy YtfE (46 μM) and [4Fe-4S] NsrR (20 μM) solution before (black line) and after the addition of 3 mM KNO₂ (red line). (B) EPR spectra of equivalent samples (100 μM deoxy YtfE and 30 μM [4Fe-4S] NsrR). NO generated by YtfE damages the [4Fe-4S] NsrR leading to DNIC formation (g = 2.03). In the absence of NsrR, MNIC YtfE (g = 3.95) was observed, along with mixed-valent YtfE. Di-ferrous YtfE in the presence of [4Fe-4S] NsrR and nitrite-treated [4Fe-4S] NsrR are shown for comparison.