The F 0 F 1 Complex

Complex V (also called ATP synthase or the F 0 F 1 complex) is a multi-protein structure with three-fold symmetry, resembling a mushroom (Figure 15.14). It consists of a top knob called F 1 and a stalk, which joins the knob to the base called F 0 in the inner mitochondrial membrane. The F 1 knob projects into the mitochondrial matrix and contains three dimers arranged like segments of an orange around the stalk. The stalk contains and proteins; is attached to protein b of the F 0 base, which also contains proteins a and c plus others. The abc complex is called a stator.

The F 1 complex is the part of complex V that synthesizes ATP as protons pass from the intermembrane space through the stalk and out the top of the F 1 complex into the mitochondrial matrix. Movement of the protons through the F 1 complex causes it to rotate (Figure 15.20). As seen in Figure 15.19, F 1 contains three similar, but not identical, binding sites for ATP or ADP + Pi. These are called L, T, and O, for Loose, Tight, and Open. The tight binding site always contains ATP. ADP and Pi can bind together in the L site. A turn of the rotor (as a result of proton movement through the complex) converts all three binding sites into new conformations. The T site becomes the O site, and ATP is released. The L site becomes a T site, which starts to condense ADP + Pi to ATP. The O site becomes an L site, which prepares to bind the next ADP + Pi. At each turn of the wheel, an ATP is released.

The antibiotic oligomycin binds to a specific protein of the F 0 complex, blocks the flow of protons through the F 0 channel, and inhibits oxidative phosphorylation directly.

See also: Chemiosmotic Coupling, Oxidative Phosphorylation