ELECTROCHEMISTRY OF CYTOCHROME-C(3) AT A LIPID-MODIFIED GRAPHITE ELECTRODE

The electron transfer reactions between a lipid-modified, pyrolytic gr aphite (PG) electrode and tetraheme cytochromes c3 have been studied a t different ionic strengths by cyclic and square-wave voltammetry. In 0.1 M phosphate buffer (pH 7.6), no signal was detected at the PG elec trode coated with a mixed layer of phosphatidylcholine (PC) and choles terol (CH) (containing 5 mg ml-1 PC). The signals corresponding to the reduction-re-oxidation of cytochrome c3 from Desulfovibrio vulgaris H ildenborough (DvH) were restored by doping the lipid layer with laurat e anions. At low ionic strengths (10 mM phosphate), using the same (PC - CH + LA)-modified PG electrode, DvH cytochrome c3 molecules are inc orporated into the lipid layer. The stability of the film has been stu died after transfer into an electrolyte solution. No incorporation was observed in the case of cytochrome c3 from Desulfovibrio desulfurican s Norway. The results support the electrostatic nature of the interact ions between cytochrome c3 and the lipid layer. This approach to the e lectrochemistry of cytochrome c3 opens new ways for the study of prote in\lipid interfaces.