Electrochemical properties of myoglobin embedded in Langmuir-Blodgett and cast films of synthetic lipids

Electrochemical parameters, formal potentials (E^o′), electron-transfer rate constants (k^o′), and diffusion coefficients (D_ct) have been determined for myoglobin (Mb) embedded in the Langmuir-Blodgett (LB) and cast films of five synthetic lipids including two types of polymeric lipids bearing ammonium or poly(ethylene glycol) as a head group. The heterogeneous electron-transfer rate constants of MbFe^III/MbFe^II in these films were ca. 10²-10³-fold larger than those for Mb in solution at an indium tin oxide electrode. Myoglobin-lipid LB films on basal-plane pyrolytic graphite (PG) electrodes gave 3-10-fold larger k^o′ values compared with cast films of the same lipid. The Mb-lipid films showed gel to liquid-crystal phase transitions consistent with bilayer structures. The peak current of the square wave voltammograms for the cast Mb-lipid films showed breaks in the phase-transition temperature regions of the corresponding lipid films. Dependence of k^o′ on lipid structure was not significant. A variety of synthetic lipids provided suitable microenvironments for the enhanced electron transfer of Mb. Immobilized Mb in the lipid films was stable for more than a month. The specific orientation of Mb in all Mb-lipid films was shown by linear dichroism. The orientation does not depend on the type of the lipids.