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

Abstract

The cytochrome bc 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) 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 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 simulations. Investigations reveal several spontaneous charge transfer modes from amino acid residues and cofactors at the Q-site to the trapped O molecule.

Quantum effects in the brain: A review

“…Both photosynthesis and mitochondrial respiration make use of an electron transport chain, which powers has published a number of papers motivated by the fact that malfunctions in the bc1 complex lead to many different diseases. They also hope to better understand photosynthesis in order to optimise energy conversion research [147][148][149] . The reduction and oxidation of ubiquinone is essential to the electron transfer reactions in cytochrome bc1 and the concentration of ubiquinone is particularly high in the high energy consumption environment of the brain 150,151 .…”

Ubiquinol treatment for TBI in male rats: Effects on mitochondrial integrity, injury severity, and neurometabolism

“…Ubiquinone (CoQ10) is produced within the mitochondrial respiratory chain and exists in three reduction‐oxidation states: (1) oxidized form (ubiquinone); (2) semiquinone (ubisemiquinone); and (3) reduced form (ubiquinol). The capacity of CoQ10 to act as a two‐electron carrier (moving between the quinone and quinol form) and a one‐electron carrier (moving between the semiquinone and one of the other forms) is central to its role in the electron transport chain and as an ROS‐scavenging antioxidant (Salo, Husen, & Solov'yov, ; Suenobu, Shibata, & Fukuzumi, ). If the mitochondrial production of ubiquinol is disrupted, ATP production is decreased, oxidative stress occurs, and apoptosis increases (Desbats, Lunardi, Doimo, Trevisson, & Salviati, ).…”

Towards predicting intracellular radiofrequency radiation effects

“…The RF magnetic field influence depends on the underlying subcellular structures and chemical processes on the molecular scale, some of which are involved in radical production. The produced radicals can appear crucial for the functioning of molecular systems [6], or become unfortunate side products as for example the superoxide produced in the bc1 complex [24, 25]. Radicals, and radical pairs in particular, can be created during vital cellular processes, and the spin dynamics of these radicals may determine the outcome of chemical processes in which they participate.…”

“…Another example is the cytochrome bc1 complex [23–27], which can be found in the mitochondrial membranes and is responsible for proton transport across the membrane as part of the respiratory chain. A recent study indicated that superoxide may be generated as a side reaction in the cytochrome bc1 complex [24, 25], and it is not unlikely that the production rate as well as its chance to escape the reaction sites within the protein complex might be affected by RF magnetic fields.…”