A. J. Moody

The Charge Translocating Reactions of the bc Complexes and Cytochrome Oxidase

The bc complex and cytochrome oxidase are two of the major respiratory electron transfer complexes of mammalian mitochondria. Their catalytic cycles result in the net translocation of a proton across the lipid bilayer, an effect which is in addition to any scalar protonic changes of the chemical reactions. The net translocation causes a charge imbalance across a region of low dielectric strength and so results in a transmembrane electric field,Δψ It should be noted, however, that the field-producing component reactions of the “proton pumping” chemistry need not involve electrogenic proton movements. Transmembrane electron transfer or movements of other charged species can be electrogenic with associated protonic changes being non-electrogenic. In all cases, measurable electrogenicity will only occur if a counter ion is unable to co-migrate, and if the medium through which the charge moves has a sufficiently low dielectric strength (figure 1A). Electrogenic movement of a charged species can occur only along such a “well”; the well interconverts chemical potential field and electric field [1,2].