Figure 5.

Physiological behavior of bc₁ dimer. For all the simulations, the cytochrome c pool was 20% reduced, matrix and cytosolic pH was 7, superoxide concentration was 100 pM, and oxygen was 30 μM. The Q pool was 20 mM and the reduced fraction and the membrane potential were variable as shown. (A) The cytochrome c reduction rates show a maximum rate when the Q pool is nearly fully reduced (∼90%) at 0 mV, which shifts to a maximum when the pool is ∼65% reduced at high membrane potentials. (B) The superoxide production simulations indicate a maximum when the Q pool is 75% reduced that shifts to ∼95% as the membrane potential approaches zero. (C) Slices through the surface of cytochrome c reduction rate (solid lines) and superoxide production rate (dashed lines) at various Q-pool redox states and membrane potentials are shown in the top two panels. In the bottom panel, the bistability stability phenomenon is shown. (D) Enzyme state occupancies for these conditions reveal that higher reduced states are achieved as both the Q pool becomes reduced and the membrane potential is high. To see this figure in color, go online.