Refuting the ideas advocated by Yuly et al. (PNAS, Sep. 2020): ‘Universal free energy landscapes’ and ‘deterministic electron-relay circuitry’ are unsustainable within membrane-embedded cytochrome b protein complexes involved in bioenergetic routines

This communication discusses the interactions/outcomes of isoprenoid quinones/quinols (Q/QH2) and membrane-bound cytochromes involved in bioenergetic routines. Particularly, we use qualitative and quantitative arguments to counter the idea that highly deterministic electron relays are triggered within Complex III of mitochondria, resulting from the donation of two electrons by QH2 (Yuly et al., PNAS, 2020). In this regard, we propose that murburn concept explains the role(s) of membrane-embedded Q/QH2 in vital metabolic processes such as mitochondrial oxidative phosphorylation (OxPhos) and chloroplastid/cyanobacterial photophosphorylations (PhotoPhos), without invoking highly fastidious universal free energy landscapes or deterministic electron circuitry.