3.D.3.1.2
Proton pumping cytochrome bc₁ complex of 3 dissimilar subunits, PetABC.  The pathway of transmembrane electron transfer has been determined and compared with that of the B₆f complex from the same organism which is strikingly different (Bhaduri et al. 2017). The cryo-EM structure of the four-subunit Rhodobacter sphaeroides cytochrome bc₁ complex in styrene maleic acid nanodiscs has been solved (Swainsbury et al. 2023). The additional subunit is called subunit IV which is one of up to eight supernumerary subunits that modify the function of the CytBC₁ complex in mitochondria (Swainsbury et al. 2023). .