eA KD 13-subunit protein complex, with structure determined in 1996 e Three subunits are probably critical to the function e Three copper ions(2 CuA, ICuB), two heme a groups(a and 3)act as electron carriers in complex IV e four electrons need to be transferred to reduce one o molecule at theFe-CuB center"(via peroxy intermediates) of complex iv to form 2 H,O e Four substrate protons are consumed from the n side for every four electrons transferred to one O molecule e One proton is pumped out from the n to p side for each electron to be transferred by an yet defined mechanism A 204 kD 13-subunit protein complex, with structure determined in 1996.  Three subunits are probably critical to the function.  Three copper ions (2 CuA, 1CuB), two heme A groups (a and a3 ) act as electron carriers in complex IV.  Four electrons need to be transferred to reduce one O2 molecule at the “Fe-CuB center” (via peroxy intermediates) of complex IV to form 2 H2O.  Four “substrate” protons are consumed from the N side for every four electrons transferred to one O2 molecule.  One proton is pumped out from the N to P side for each electron to be transferred by an yet defined mechanism