Identification of the axial heme ligands of cytochrome b556 in succinate: Ubiquinone oxidoreductase from Escherichia coli

Abstract
Electron paramagnetic resonance (EPR) and near‐infrared magnetic circular dichroism (MCD) have been used to identify the ligands to the cytochrome b 556 component of succinate: ubiquinone oxidoreductase (succinate dehydrogenase) from Escherichia coli. The ‘highly axial low spin’ (HALS) EPR spectrum suggests bis(histidine) ligation of the heme with the histidines in a staggered configuration. The near‐infrared MCD spectrum exhibits a low energy maximum at 1600 nm which is also clearly indicative of bis(histidine) ligation of the heme iron. The data unambiguously demonstrate that the heme b 556 is ligated to E. coli succinate dehydrogenase via two histidines.

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