Cytochrome bc1 Complex (Qi Site)

The Qi site of the cytochrome bc1 complex (Complex III) is the quinone reduction site located on the matrix side of the inner mitochondrial membrane or bacterial plasma membrane. It plays a crucial role in the Q-cycle mechanism by accepting two electrons from heme bH and two protons to reduce quinone to quinol. This process is essential for electron transport and proton translocation, contributing to the proton-motive force required for ATP synthesis. The Qi site is a target for several inhibitors, including antimycin A and NQNO, and is considered a promiscuous drug target due to its ability to accommodate various chemical scaffolds. Targeting the Qi site has therapeutic potential against pathogens, but resistance mutations are a concern.

Other names

Complex III Qi siteUbiquinol:cytochrome c oxidoreductase Qi siteQuinone reduction site of Cytochrome bc1 complex

Inhibition of quinone reduction at the Qi site of the cytochrome bc1 complex, disrupting electron transport and ATP synthesis.