<P> This complex is inhibited by Carboxin . </P> <P> In Complex III (cytochrome bc complex or CoQH - cytochrome c reductase; EC 1.10. 2.2), the Q - cycle contributes to the proton gradient by an asymmetric absorption / release of protons . Two electrons are removed from QH at the Q site and sequentially transferred to two molecules of cytochrome c, a water - soluble electron carrier located within the intermembrane space . The two other electrons sequentially pass across the protein to the Q site where the quinone part of ubiquinone is reduced to quinol . A proton gradient is formed by one quinol (2 H 2 + e − (\ displaystyle (\ ce (2H + 2e -)))) oxidations at the Q site to form one quinone (2 H 2 + e − (\ displaystyle (\ ce (2H + 2e -)))) at the Q site . (in total four protons are translocated: two protons reduce quinone to quinol and two protons are released from two ubiquinol molecules). </P> <Dl> <Dd> QH 2 + 2 cytochrome c (Fe III) + 2 H + (in) ⟶ Q + 2 cytochrome c (Fe II) + 4 H + (out) (\ displaystyle (\ ce (QH2 + 2 cytochrome c (Fe ^ (III)) + 2 H+ (in) -> Q + 2 cytochrome c (Fe ^ (II)) + 4 H+ (out)))) </Dd> </Dl> <Dd> QH 2 + 2 cytochrome c (Fe III) + 2 H + (in) ⟶ Q + 2 cytochrome c (Fe II) + 4 H + (out) (\ displaystyle (\ ce (QH2 + 2 cytochrome c (Fe ^ (III)) + 2 H+ (in) -> Q + 2 cytochrome c (Fe ^ (II)) + 4 H+ (out)))) </Dd>

Where are the integral membrane proteins of the electron transport chain located