Abstract
In recent studies we reported that dicyclohexylcarbodiimide (DCCD) inhibited proton translocation in ubiquinol:cytochrome c oxidoreductase (cytochrome bc1complex) from yeast mitochondria where it was bound to aspartate-160 of cytochrome b. In the current study, we report that DCCD and its fluorescent analogue,N-cyclohexyl-N′-[4-(dimethylamino)naphthyl]carbodiimide (NCD-4), inhibit 50–60% proton pumping in the cytochrome bc1complex of the bacteriumRhodobacter sphaeroideswith a 20% inhibition of electron transfer activity. Radioactive DCCD is bound exclusively to cytochrome b at aspartate-187, which is located at the C-terminal region of the CD loop connecting membrane-spanning helices C and D of cytochrome b. Fluorescent studies with NCD-4 revealed that aspartate-187 is located in a mildly hydrophobic pocket in the bc1complex at a distance of 2–3 Å from the surface of the membrane.
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