Figure 7: A general kinetic scheme for the actomyosin ATPase cycle.
From: Structural basis for drug-induced allosteric changes to human β-cardiac myosin motor activity
The myosin motor domain (M, blue) is shown at the top left at the end of the cycle, tightly bound to actin (A, red) in the nucleotide-free rigour state (A·M). ATP binds rapidly and releases the MD from actin. The MD then undergoes a conformational equilibrium before ATP hydrolysis between two states designated as M↓ and M↑. These states correspond to the near-rigour (M↓) and pre-power stroke (M↑) conformations. The arrows indicate the down position of the LAH (M↓) and the up position in the pre-power stroke state (M↑) and correlate with intrinsic fluorescent states. The ‘Recovery Stroke’ is the rapid equilibrium (KRS) between these states. The hydrolysis equilibrium (KH) is coupled to this transition before binding to actin6. On rebinding to actin the weak to strong transition is coupled to γ-phosphate (Pi) release. This results in a conformation change triggering rotation of the LAH producing the ‘Power Stroke’ and force production. Rapid ADP dissociation follows, completing the cycle. OM influences the hydrolysis equilibrium (KH), and it accelerates Pi release associated with the weak to strong actin-binding transition6. These steps are boxed with dotted lines.
