The cycle of ATP-ADP-Pi- acto-myosin.

The CB cycle was subdivided into seven different conformational states, with three detached states (D1, D2, and D3) and four attached states (A1, A2, A3 and A4). Transition A4 → D1 was the ATP binding step; D1 was the first detached step. CB detachment occurred when ATP bound to the actin (A)—myosin (M) complex (AM). The rate constant for detachment was g₂; AM + ATP → A + M-ATP. Transition D1 → D2 was the ATP hydrolysis step; M-ATP → M-ADP-Pi. Transition D2 → D3 was M-ADP-Pi → M*-ADP-Pi. D3 was the step having the highest probability. Transition D3 → A1 was the weakly bound attachment state: the myosin head (M*-ADP-Pi) weakly bound to A. The rate constant for attachment was f₁; M*-ADP-Pi + A→ AM-ADP-Pi. Transition A1 → A2 was the power stroke or strongly bound state which was triggered by the Pi release: AM-ADP-Pi → AM-ADP + Pi. Transition A2 →A3 was the release of ADP: AM-ADP → AM + ADP. A4 was a transitory attached step (AM) having the lowest probability and preceeding the detachment step D1 induced by the attachment of a new ATP molecule.