evolutionary conserved Q-cycle

  4 H+ per e- pair CoQH2 thru Complex III

1.    CoQH2 binds to Qo site outer site
2a.  releases 2H+ into perimito space
2b.  1e- passed to Cyto-C via an FeS
3.    1e- passes to cytoBL-->BH
           & reduces CoQ at matrix Qi site
4.    oxidized CoQH2 dissociates at Qo site
5.    2nd CoQH2 binds to open Qo
6a.  repeat of step 2a.
6b.  repeat of step 2b.
7.    repeat of step3.
8.    2H+ of matrix reduce CoQ --> CoQH2
9.    CoQH2 dissociates from Qi site
10.  open Qi site binds new CoQ