Effect of funiculosin and antimycin A on the redox-driven H+-pumps in mitochondria: on the nature of "leaks'.

The effect of antimycin A and funiculosin, two inhibitors which block electron transfer in the b-c1 complex, on electron flow and electrochemical potential difference of H+ ions in mitochondria at static head (state 4) is investigated. In addition, the respiratory control ratio is determined as the ratio between uncoupler stimulated and static-head electron flow. Malonate, a competitive inhibitor or succinic dehydrogenase, is used for comparison. All three inhibitors cause an extensive depression of static-head electron flow but only a limited decrease in the electrochemical potential difference of H+ ions. With the antimycin-type of inhibitors, the respiratory control ratio slightly increases up to about 50% inhibition of electron flow and then steeply declines. With malonate, a strong decrease of the respiratory control ratio is observed in a concentration range where the electron flow is inhibited less than 10%. It is shown than the data do not comply with the generally accepted hypothesis of a leak conductance being regulated by the electrochemical potential difference of H+ ions. They can be interpreted in terms of not tightly coupled redox-driven H+-pumps. A non-vanishing electron flow at static head then arises predominantly from molecular slipping in the pumps, and the (constant) leak conductance yields only a minor contribution.