The electron transport system present in the photosynthetic apparatus and respiratory chain were evolutionary acquisitions that allowed the organisms to convert electromagnetic energy in chemical energy and thus improve the use of energy fuels. These systems acquired by prokaryotes were preserved in the highly complex organisms always with the participation of the cytochromes. Since the discovery of the cytochromes, and the isolation and association of these proteins to model membranes, the liposomes, have been used to investigative strategies to characterize the structure and function of these proteins. From these studies important findings have contributed to the comprehension of the energy transduction mechanisms and the role played by the nonredox subunits present in the protein complexes of the respiratory chain of eukaryotes.