We note that in the model above, the two negative charges (formed after two electron reduction of Q) are reorganized such that one remains on the Q molecule and another one on the protein (in the form of X). One key question is whether these anionic species have longenough lifetimes to drive pumping. The precise identities and nature of the gates and valves necessary to prevent premature annihilation of these anionic species are currently unknown, but remain an active area of research.