Studies on the mechanism of electron transport in the bc1-segment of the respiratory chain in yeast. II. The binding of antimycin to mitochondrial particles and the function of two different binding sites.

1. In mitochondrial particles antimycin binds to two separate specific sites with dissociation constants KD1 less than 4 - 10(-13) M and KD2 = 3 - 10(-9) M, respectively. 2. The concentrations of the two antimycin binding sites are about equal. The absolute concentration for each binding site is about 100 - 150 pmol per mg of mitochondrial protein. 3. Antimycin bound to the stronger site mainly inhibits NADH-and succinate oxidase. Binding of antimycin to the weaker binding site inhibits the electron flux to exogenously added cytochrome c after blocking cytochrome oxidase by KCN. 4. Under certain conditions cytochrome b and c1 are dispensible components for antimycin-sensitive electron transport. 5. A model of the respiratory chain in yeast is proposed which accounts for the results reported here and previously. (Lang, B., Burger, G., and Bandlow, W. (1974) Biochim. Biophys. Acta 368, 71-85).