Most living cells acquire their energy through photosynthesis or respiration, both of which convert input energy (sun light or food, respectively) through coupled electron and proton transfer processes. A key role is played here by a protein, called the bc₁ complex, that intermediately stores energy through the reaction of molecules of quinol into molecules of quinones, utilizing energy released to pump protons across an intracellular membrane. This reaction is initiated in the bc₁ complex at the site of binding of the quinol molecule, but critical details about the physical mechanism leading to coupled electron-proton transfer are still unknown. A recent study, based on molecular modeling with NAMD and quantum chemistry calculations, investigated possible reaction mechanisms in case of the bc₁ complex from the bacterium Rhodobacter capsulatus. The calculations suggest a novel configuration of amino acid residues responsible for quinol binding in the bc₁ complex, and support a mechanism for coupled proton-electron transfer from quinol to iron-sulfur cluster. The study opens the door for a complete simulation description of the crucial role of the bc₁ complex in bioenergetics. More about the bc₁ complex can be found here.