Inhibition of the Links between Electron Transfer and Proton Translocation in Mitochondria

The mechanism by which proton extrusion is linked to electron transfer in mitochondria was investigated by means of the primary amine‐specific reagent fluorescamine, and of compounds obtained from the reaction of fluorescamine with simple amines (e.g. benzylamine) and with the mycosamine‐containing antibiotic amphotericin B. The effect of these ‘modifiers’ (i.e. fluorescamine and the acyclic amine‐fluorescamine compounds) on the activities of sites II and III of the electron transfer chain were assayed separately using specific inhibitors to block the action associated with the other site. Both types of modifiers inhibited the proton extrusion across the membrane to a significantly greater extent than the electron transfer process in both sites II and III. In contrast, the lactone derivative (or cyclic form) of the amine‐fluorescamine compounds had no significant inhibitory effect on the proton extrusion and its associated electron transfer. These results are consistent with the hypothesis that the link between proton extrusion and electron transfer in mitochondria is indirect in nature. The results show that: (a) the links involved in sites II and III are identical or very similar in nature; (b) a covalent modification of primary amino groups in the inner membrane is not essential for the expression of these differential inhibitory effects; (c) specific structural features in the amine‐fluorescamine compounds, and in the mitochondria‐fluorescamine derivatives, are crucial for the expression of the inhibitory effects. Our results contradict the ‘redox loop’ model of Mitchell, and are compatible with the proton pump concept for the linked proton translocation in oxidative phosphorylation.