Cytochrome c3, an oriented iron wire

The kinetics of reduction and ligand binding by the cytochromes c ₃ are reported on as part of an ongoing effort to understand the unique electrical properties of this unusual heme protein family. When absorbed as films on electrode surfaces they show conductivity changes of ten orders of magnitude when the iron redox state is changed. The studies presented establish that both carbon monoxide binding and deazariboflavin semiquinone reduction enable the hemes of cytochrome c ₃ to be discriminated and offer the opportunity of characterizing the interaction domains and immediate heme environment of each of the hemes. This may provide the means for investigating the interactions between the hemes. The approaches described here, coupled with the use of cytochrome c₃ from other species (natural chemical modification) and site-directed mutagenesis, should allow one to understand in molecular terms those properties of cytochrome c₃ that result in its unique behavior in dry films