Figure 1.

Mössbauer spectra of WT and C32S mutant of PqqE. ⁵⁷Fe Mössbauer spectra of (A) ⁵⁶Fe‐as‐purified WT enzyme reconstituted with ⁵⁷Fe, (B) ⁵⁷Fe‐as‐purified WT enzyme reconstituted with ⁵⁶Fe, (C) ⁵⁷Fe‐as‐purified WT enzyme reconstituted with ⁵⁷Fe, and (D) ⁵⁷Fe‐as‐purified C32S mutant reconstituted with ⁵⁷Fe, all recorded at 5 K. Simulated spectra are shown as follows: blue, [4Fe–4S]²⁺; green, [2Fe–2S]²⁺; gray and light blue, ferrous and ferric sites, respectively, of the [4Fe–4S]²⁺ cluster ligated with the side‐chain carboxyl group of Asp319 at the Aux II site; red, free (noncluster) high‐spin Fe²⁺; black, the sum of the simulated spectra.