Fig. 2.

Schematic representation of the three-state MG model where each Tm–Tn complex is assumed to cover seven actin sites. The complete kinetic diagram for the binding of S1 to a structural actin₇·TmTn unit includes seven actin monomers. The resulting model contains one blocked state, eight closed states and 36 open states. All states are denoted as numbers in the square boxes (gray). The configurations of some states are shown. The fused two-way arrows represent the transitions from the blocked to the closed state with equilibrium rate transition constant, K_b, and the transition from closed to open state with the rate K_t. The two-way arrows represent forward and backward transition rates between myosin states interacting with actin: (i)S1 from solution weakly binding to actin (into A-state) and (ii) transition from A-state to R-state. The forward rate of S1 binding from the solution to the actin in an actin7-TmTn is defined as effective binding rate k₊₁ c (s⁻¹) multiplied by the number of unoccupied actin monomers within the unit, and the backward rate of the S1 unbinding from A-state back to solution by detachment constant k₋₁ multiplied by the number of S1 bound in A-state in the actin₇·TmTn. Similarly, transition from A-state to R-state is defined by forward constant k₊₁ c (s⁻¹) multiplied by the number of S1 bound in A-state in the actin₇·TmTn, and transition from R-state to A-state is defined by backward rate constant k-1 multiplied by the number of S1 bound in R-state in the unit.