[A three-cycle mechanism of the respiratory chain]

A scheme of the respiratory chain is presented, according to which three delta mu H-generators (complexes I, III and IV) provide for the transmembrane transport of ten H+ ions per atom of adsorbed O2. It is assumed that all the three delta mu H-generators operate in accordance with the same mechanism, namely, they translocate electrons at a distance averaging 1/2 of membrane width, whereas protons moving in the opposite direction pass the other halfwidth across the membrane. A redox cycle functions in each of the three sites of the energy coupling mechanism: the flavin (F) cycle in complex I, the Q-cycle in complex III and the O-cycle in complex IV. These cycles are interconnected by mobile carriers: the F- and Q-cycles by ubiquinone and the Q- and O-cycles by cytochrome c.