FIGURE 5.

Iron or zinc is coordinated by C67-C128-H46-H57. A, superposition of the ¹H-¹⁵N-HSQC spectra of NarE (yellow), NarE containing 1 mm DTT (red), and NarE with 1 mm DTT and an equivalent amount of FeCl₃ (blue). B, residues whose NMR signals are attenuated by more than 50% or show a combined chemical shift dispersion Δδcomb > 0.03 after addition of FeCl₃ are mapped in blue onto the NarE structure. NarE four cysteines as well as His-46/His-57 are highlighted. Cys-67 and Cys-128 are affected by the binding of iron while Cys-11 and Cys-130 (green) remain unaffected. C, superposition of the ¹H-¹⁵N-HSQC spectra of NarE containing 1 mm DTT (red) and NarE with 1 mm DTT and an equivalent amount of ZnCl₂ (blue). D, residues whose NMR signals where attenuated more than 50% or show a combined chemical shift dispersion Δδcomb > 0.03 after addition of ZnCl₂ are mapped in blue onto the NarE structure. The NarE four cysteines as well as His-46/His-57 are highlighted. Cys-67 and Cys-128 as well as His-46/His-57 are affected by the binding of zinc while Cys-11 and Cys-130 (green) are unaffected.