Dicyclohexylcarbodiimide blocks proton ejection and affects antimycin binding but not electron transport in complex III from yeast mitochondria.

Treatment of complex III with dicyclohexyldicarbodiimide (DCCD) either before or after incorporation into liposomes resulted in a loss of electrogenic proton movements; however, only minimal decreases in cytochrome c reductase activity were noted in the liposomes containing DCCD-treated complex III. Thus, DCCD appears to act by "uncoupling" proton translocation from electron transport. A decreased sensitivity of the ubiquinol:cytochrome c reductase activity to antimycin was also noted in the DCCD-treated complex III. This loss of sensitivity to antimycin was reflected in a decreased binding of antimycin to the complex after DCCD treatment from 9.5 nmol/mg of protein in the control to 3.8 nmol/mg of protein in the DCCD-treated complex. DCCD also affected the red shift observed after antimycin addition to dithionite-reduced complex III resulting in a broad peak with no sharp maximum. Similarly, DCCD treatment of yeast mitochondria resulted in a complete loss in the red shift after antimycin addition to mitochondria previously reduced with succinate. No loss in enzymatic activity was observed in the DCCD-treated mitochondria. These results suggest that DCCD concomitant with the inhibition of proton ejection in the cytochrome b-c1 region of the respiratory chain causes modifications in the properties of cytochrome b which alter the binding of antimycin without significantly affecting the electron transfer activity of this cytochrome.