Fig. 4. Kinetics of antimycin binding to center N in the presence of center P inhibitors.

Antimycin (20 µM) binds in a single phase in the presence of 1.2 equivalents of myxothiazol per bc₁ monomer, present at a concentration of 2.5 µM (panel A) and in two phases in the presence of stigmatellin (panel B). The relative contribution of each kinetic phase in panel B is shown in parentheses next to its rate. The single rate observed with myxothiazol bound at center P is linearly dependent on the concentration of antimycin (panel C). With stigmatellin occupying the center P sites (panel D) binding of antimycin is concentration-dependent during the first kinetic phase (filled red circles and solid red line), but is concentration-independent during the slow second phase (open red circles, dotted red line), indicating that a conformational change limits binding of antimycin to half of the center N sites when stigmatellin is occupying both center P sites in the dimer. Data reproduced from Ref. 36.