Figure 2.

SDUF reactions under Catalytic conditions generate [2Fe-2S]²⁺ clusters in the absence of DTT and [4Fe-4S]²⁺ clusters in the presence of DTT (Mössbauer experiment M1). (A) LC–ICP-MS chromatogram (⁵⁷Fe detection) of reaction mixtures without (black) and with (red) DTT. The inset shows the absorbance spectrum of the DTT-free fraction at 17.6 mL (arrow). (B) Mössbauer spectrum (5 K, 0.05 T, parallel) of the DTT-free sample prior to LC–ICP-MS analysis. Green and blue lines are quadrupole doublets due to HS Fe²⁺ with S-based (80%) and O/N-based donors (12%), respectively. Arrows indicate a 5% contribution from a doublet due to [2Fe-2S]²⁺ clusters. (C) M1 Mössbauer spectrum (5 K, 0.05 T, parallel) of the reaction mixture containing 10 mM DTT. The green line is a quadrupole doublet due to HS Fe²⁺ with likely S coordination (85% of the spectral intensity). Arrows indicate a quadrupole doublet (10% intensity) due to [4Fe-4S]²⁺ clusters. (D and E) Same as panels B and C, respectively, after subtracting the quadruple doublets due to HS Fe²⁺. Red lines are simulations of the quadrupole doublets due to [2Fe-2S]²⁺ and [4Fe-4S]²⁺ clusters. Mössbauer parameters are listed in Table 1.