- A: alpha bundles
- X: a domain/subunit of cytochrome bc1 complex (Ubiquinol-cytochrome c reductase)
- H: a domain/subunit of cytochrome bc1 complex (Ubiquinol-cytochrome c reductase)
- T: a domain/subunit of cytochrome bc1 complex (Ubiquinol-cytochrome c reductase)
- F: Cytochrom_B_C