Fig. A2.

Kinetic scheme of the 4-state model. A: the full kinetic scheme. Myosin starts strongly bound to actin (state 1) and then releases ADP in a force-dependent process to enter the rigor state (state 2). Detachment in a post-power stroke state (state 3) occurs upon ATP binding. Reversible ATP hydrolysis allows myosin to enter a detached pre-power stroke state (state 4) from which attachment can occur, allowing myosin to enter state 1 and the cycle to continue. B: a reduced kinetic scheme, given a sufficiently high ATP concentration. At high ATP concentrations, the lifetime of state 2 is negligible, and detachment is limited by force-dependent ADP release. D, ADP; P, inorganic phosphate; T, ATP.