Cytochrome c₃ Modified Artificial Liposome. Structure, Electron Transport, and pH Gradient Generation

Detailed studies on the structure, electron transport rates, and proton transport rates coupled to electron transport were carried out for artificial lecithin liposomes functionalized with cyt c₃ or cyt c. Artificial liposomes modified with cyt c₃ were found to be single-walled, normal liposomes of ca. 250-Å diameter based on electron micrographs. The electron transport rate across the membrane was very much accelerated in the presence of cyt c₃, and the electron influx was coupled with rapid proton transport from the outside to the inside of the artificial liposome, generating a large pH gradient across the membrane. The maximum pH gradient is determined by the accelerated proton influx and slower passive proton efflux. The permeability coefficients of passive proton flow, P_H⁺, and of accelerated coupled proton flow, P_H⁺, were estimated. The observed permeability for the coupled transport is by a factor of l0¹-l0² larger than the usual passive proton permeability.