Charge Transfer at the Qo-Site of the Cytochrome bc1 Complex Leads to Superoxide Production

The cytochrome be, complex is the third protein complex in the electron transport chain of mitochondria or photosynthetic bacteria, and it serves to create an electrochemical gradient across a cellular membrane, which is used to drive ATP synthesis. The purpose of this study is to investigate interactions involving an occasionally trapped oxygen molecule (O-2) at the so-called Q site of the bc, complex, which is one of the central active sites of the protein complex, where redox reactions are expected to occur. The investigation focuses on revealing the possibility of the oxygen molecule to influence the normal operation of the bc(1) complex and acquire an extra electron, thus becoming superoxide, a biologically toxic free radical. The process is modeled by applying quantum chemical calculations to previously performed classical molecular dynamics Investigations reveal several spontaneous charge transfer modes from amino acid residues and cofactors at the Q(omicron)-site to the trapped Q(2) molecule.