Direct electrochemistry of bovine heart cytochrome c facilitated by cysteine derivatives and analogues. Some effects of facilitator structure

Abstract.

Bovine heart cytochrome c electrochemistry was investigated by cyclic voltammetry using gold electrodes modified by self-assembled monolayers of cysteine and some of its derivatives, including glutathione. Glutathione shows a peculiar dependence of the facilitating ability on the oxidation state of the sulfur functionality. Whereas the disulfide form acts as an efficient facilitator, the thiol form is completely inactive. This behavior was accounted for by the lower stability of adsorbed thiol layers as compared to disulfide layers. Apparently, small molecules of cysteine derivative form rather stable adsorbed layers with a high degree of dimer formation. Conversely, reduced glutathione is not able to turn into the disulfide form in the adsorbed layer. Consequently, only the layer produced by the adsorption of the disulfide form itself is stable enough for promoting direct electron transfer reactions of cyt c.