CONTROL OF THE ELECTRON-TRANSFER REACTIONS BETWEEN C-TYPE CYTOCHROMESAND LIPID-MODIFIED ELECTRODES

The electron transfer reactions between a lipid-modified pyrolytic gra phite (PG) electrode and four c-type cytochromes (monoheme cytochrome c and cytochrome c553 from Desulfovibrio vulgaris Hildenborough, tetra heme cytochromes c3 from D. vulgaris Hildenborough and D. desulfurican s Norway) have been studied by cyclic and square-wave voltammetry. No signal was detected at the PG electrode simply coated with a mixed lay er of phosphatidylcholine (PC) and cholesterol (CH). The peaks corresp onding to the reduction-reoxidation of cytochrome C553 were restored b y doping the lipid layer with laurate anions (LA). In the case of cyto chrome c, a rapid electron transfer reaction has been observed at the (PC-CH + LA)-modified PG electrode, accompanied by the progressive inc orporation of protein molecules. By studying the effect of pH on the c v peak heights, it has been shown that the profiles for the four cytoc hromes depend on the protonation of the laurate anions and the protona tion-deprotonation of protein species. The results support the electro static nature of the interactions between the cytochrome and the lipid layer but other factors (eg hydrophobic effects) are not excluded.