Figure 4.

The complete crossbridge cycle. Incorporation of ATP shifts the head from the strong binding state (a) into the weak binding state (b). Detachment and reattachment result in another weak binding state (c) at another actin position with a conformation optimal for the power stroke. To save space, diagrams c and d are shifted to the right compared with their true alignment relative to a and b. The transition to the strong binding state (d) (power stroke) stretches the elastic element E2, and allows Pi to escape. Transfer of the free energy stored in E2 to the filaments takes the system back to a and results in the exchange of ADP for ATP.