Stepping rotation of F(1)-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° 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° 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.