APPLICATION OF EXCITON COUPLING THEORY TO THE STRUCTURE OF MITOCHONDRIAL CYTOCHROME-B

The circular dichroism of the reduced bis-heme mitochondrial cytochrome b in the Soret region has been analyzed using exciton theory. The theory was applied to a geometric model that reflects the current consensus of the structure of this membrane protein [Degli Esposti, M., De Vries, S., Crimi, M., Ghelli, A., Patarnello, T., & Meyer, A. (1993) Biochim. Biophys. Acta 1143, 243-271]. The analysis suggests that the iron-iron distance is about 19.5 angstrom, with a possible range of 17-23 angstrom; the two hemes appear to be canted at 45-degrees with respect to one another. It appears that the two hemes undergo a relative angular displacement upon reduction, suggesting some flexibility in the protein structure. Some applications of this analysis to other bis-heme proteins are considered.