- A: a+b complex topology
- X: Succinate dehydrogenase/fumarate reductase flavoprotein, catalytic domain
- H: Succinate dehydrogenase/fumarate reductase flavoprotein, catalytic domain
- T: Succinate dehydrogenase/fumarate reductase flavoprotein, catalytic domain
- F: FAD_binding_2