ELLIPSOMETRY OF CYTOCHROME-C ON GOLD SURFACES - EFFECT OF 4,4'-DIPYRIDYL DISULFIDE

Ellipsometry has been used to study the mode of adsorption of horse heart cytochrome c on gold in the presence and absence of the promoter 4,4'-dipyridyl disulfide. In the absence of 4,4'-dipyridyl disulfide, cytochrome c unfolds on the surface and forms an irreversibly adsorbed layer that completely covers the electrode. Adsorbed cytochrome c can mediate the reduction of cytochrome c in solution via electron transfer through the unfolded protein layer; the oxidation of cytochrome c in solution was not observed. On gold modified with 4,4'-dipyridyl disulfide, Cytochrome c adsorbs irreversibly but retains its native configuration. Ellipsometry and charge transfer measurements show that the layer of adsorbed cytochrome c completely covers the gold surface in the presence of the promoter. Both the reduction and oxidation of cytochrome c in solution occurs through the adsorbed protein layer on the modified surface. These results show that 4,4'-dipyridyl disulfide plays a key role in preventing the unfolding of adsorbed cytochrome c at the electrode solution interface.