Earth History Research Center

Figure 2. The molecular structure of the F0 subunit of the ATP Synthase complex found in the bacterial outer membrane. The F0 complex has three parts, here labeled a, b and c. The first of these, "a", consists of a single protein that spans the membrane eight times. The second unit, "b", consists of two subunits that pass through the membrane once. The third unit, "c", is present in 9 to 12 copies that each span the membrane twice.  Together the c units form a "rotor" with a hollow cylindrical center.