View article

Aquifex aeolicus, a hyperthermophilic and microaerophilic bacterium, obtains energy for growth from inorganic compounds alone. It was previously proposed that one of the respiratory pathways in this organism consists of the electron transfer from hydrogen sulfide (H₂S) to molecular oxygen. H₂S is oxidized by the sulfide quinone reductase, a membrane-bound flavoenzyme, which reduces the quinone pool. We have purified and characterized a novel membrane-bound multienzyme supercomplex that brings together all the molecular components involved in this bioenergetic chain. Our results indicate that this purified structure consists of one dimeric bc₁ complex (complex III), one cytochrome c oxidase (complex IV), and one or two sulfide quinone reductases as well as traces of the monoheme cytochrome c₅₅₅ and quinone molecules. In addition, this work strongly suggests that the cytochrome c oxidase in the …