Percolative Conduction in Biological Conductor: Cytochrome c3 Anhydrous Film of Desulfovibrio vulgaris, Miyazaki Strain

Electrical conductivity of the thin film of cytochrome c 3 , electron carrier protein of anaerobic bacteria, was measured as a function of ferri- to ferro-ratio. At the initial reduction stage of ferric cytochrome c 3 , the conductivity was gradually increased and was explained by doping effect. This was the first observation of doping effect for biological molecules. At 0.95 ferro-ratio, the conductivity was abruptly increased. The observation was analysed by the percolation theory which predicts that there is very strong heme-heme interaction between fully reduced cytochrome c 3 molecules in a condensed phase. The anomalous physico-chemical behaviors of ferrocytochrome c 3 film such as very low ionization potential and intermolecular heme-heme interaction observed by Mössbauer spectroscopy were also discussed in relation to the present results.