Ion-transport chain of cytochrome oxidase: the two chain-direct coupling principle of energy coupling.

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Abstract
Cytochrome oxidase (EC 1.9.3.1.) couples the aerobic oxidation of ferrocytochrome c to the cyclical transport of monovalent cations or to the active transport of monovalent and divalent cations. This transport capability is mediated by an intracomplex ion-transport chain of 2 protein-bound molecules of cardiolipin/molecule of cytochrome oxidase. Cardiolipin in a 2-phase system shows the identical ionophoric pattern as does the cytochrome oxidase coupled system. A molecular model of the cardiolipin chain suggests the possibility of a cage-like structure through which cations can be transferred from phosphate group to phosphate group. The ion-transport chain and the electron-transport chain are anchored to the same set of subunits (I + IV); the close proximity of the 2 chains argues for the direct coupling of electron and cation flow. The ion-transport chain of cytochrome oxidase provides an introduction to the molecular mechanisms by which ions are moved across membranes in energy-coupling systems.

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