Stepping rotation of F1-ATPase visualized through angle-resolved single-fluorophore imaging.

Orientation dependence of single-fluorophore intensity was exploited in order to videotape conformational changes in a protein machine in real time. The fluorophore Cy3 attached to the central subunit of F(1)-ATPase revealed that the subunit rotates in the molecule in discrete 120 degrees steps and that each step is driven by the hydrolysis of one ATP molecule. These results, unlike those from the previous study under a frictional load, show that the 120 degrees stepping is a genuine property of this molecular motor. The data also show that the rate of ATP binding is insensitive to the load exerted on the rotor subunit.