Circular dichroic evidence for a conformational change in a cytochrome b--c1 complex by uncoupling agents.

Circular dichroic spectra of the cytochrome b--c1 complex exhibit bilobe formation typical of exciton splitting in the presence of uncoupler. Bilobe formation occurs if both cytochrome c1 and cytochrome b are fully reduced. The fully oxidized and ascorbate-reduced complexes are not altered dichroically by uncouplers. The exciton splitting induced by uncoupler is consistent with heme--heme interaction: specifically, interaction between the two cytochromes b in the complex.