Protonic and cationic changes during cyclical cation transport driven by electron transfer

Abstract Complexes I and III in mitochondrial particles mediate the coupling of electron transfer (NADH → Q; QH 2 → ferricytochrome c ) to either cyclical or net transport of K + . Cyclical transport was characterized by a U-shaped profile for the protonic and cationic changes observed during an oxygen pulse. The K + e and H + e ratios were found to be unity for the coupled reactions mediated by Complexes I and III. Protons were released on the side of the inner membrane where oxidation was initiated (I side) and taken up on the side where oxidation was terminated (M side). The pattern now shown to be general for the three electron transfer complexes that collectively carry out the NADH → O 2 sequence includes dehydrogenation of the primary reductants on the I side, hydrogenation of the terminal acceptors on the M side, and nonergized transfer of a proton from the I to the M side of the membrane by cation/proton exchange. From these data it has been concluded that the movements of the electron and cation are coupled and synchronized, whereas the proton plays no direct role in energy coupling mediated by electron transfer complexes.