Spectroscopic identification of the axial ligands of cytochrome b560 in bovine heart succinate‐ubiquinone reductase

Abstract
The axial ligands of low potential cytochrome b560 in the five subunit bovine heart succinate-ubiquinone reductase complex and in the isolated quinone binding proteins have been investigated using EPR and near-infrared magnetic circular dichroism spectroscopies. The results are consistent with bis-histidine ligation with near-perpendicular imidazole rings for cytochrome b560 in the four-subunit complex. The pronounced changes in EPR properties that accompany isolation of the cytochrome-b560 containing quinone binding proteins, are attributed to perturbation of the orientation of the imidazole rings of the heme bis-histidine ligands, rather than a change in axial ligation.

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