Figure 1.

Effect of the axial position of an attached myosin head on the equilibrium and rate constants for steps in the cross-bridge cycle. (a) The attachment and detachment of heads to actin. $K_a^{\text{'}}$ (solid line) $k_a^{\text{'}}$ (dotted line) are the first-order equilibrium and rate constant for the attachment of pretensing heads at 1 mM actin, and k_d is the rate constant for the detachment of pretensing heads (dashed line). Attachment and detachment were calculated for the symmetric mode. (b) The tensing steps and the detachment of posttensing heads. k_tens1 and k_tens2 are the rate constants of the forward first and second tensing steps (black and gray lines, respectively), k_-tens1 and k_-tens2 are the rate constants of reverse first and second tensing steps (black and gray dotted lines, respectively), and k_i is the rate constant of detachment of posttensing heads from actin (black dotted line).