A clarification of the effects of DCCD on the electron transfer and antimycin binding of the mitochondrial bc1 complex.

We have studied in detail the effects of dicyclohexylcarbodiimide (DCCD) on the redox activity of the mitochondrial bc1 complex, and on the binding of its most specific inhibitor antimycin. An inhibitory action of the reagent has been found only at high concentration of the diimide and/or at prolonged times of incubation. Under these conditions, DCCD also displaced antimycin from its specific binding site in the bc1 complex, but did not apparently change the antimycin sensitivity of the ubiquinol-cytochrome c reductase activity. On the other hand, using lower DCCD concentrations and/or short times of incubation, i.e., conditions which usually lead to the specific inhibition of the proton-translocating activity of the bc1 complex, no inhibitory effect of DCCD could be detected in the ubiquinol-cytochrome c reductase activity. However, a clear stimulation of the rate of cytochrome b reduction in parallel to an inhibition of cytochrome b oxidation has been found under these conditions. On the basis of the present work and of previous reports in the literature about the effects of DCCD on the bc1 complex, we propose a clarification of the various effects of the reagent depending on the experimental conditions employed.