Figure 4.

Low temperature Mössbauer spectra of [2Fe-2S] cluster-bound reconstituted AtNfu2 (A) and [4Fe⁵⁷-4S] cluster-bound as-reconstituted AtNfu2 (B). Spectra were recorded at 4.2 K with a weak magnetic field of 50 mT applied parallel to the direction of γ-radiation. The black solid lines overlaid on the experimental spectra (vertical bars) are simulations based on mixtures of [2Fe-2S]²⁺ and [4Fe-4S]²⁺ clusters (red and blues lines, respectively), with each comprised of two equal intensity doublets using the parameters listed in Table 1. The [2Fe-2S]²⁺ and [4Fe-4S]²⁺ cluster components in (A) account for 85% and 15% of the total Mössbauer absorption, respectively. [4Fe-4S]²⁺ clusters account for 100% of the Mössbauer absorption in (B).