Figure 8.

Free energy diagrams of the structural and biochemical states

A, free energy diagrams of the four structural states of the myosin motor in the AM.ADP.P_i state, attached to the actin monomer either, A (continuous lines) or A′ (dashed lines). The thickness of the line identifies the progression of the state transitions, from M₁, thinnest line, to M₄, thickest line. x is zero in correspondence of the free energy minimum of a myosin motor attached to A in the M₁ state. Horizontal lines show the free energy of the detached states. B, free energy diagrams of the myosin motor attached to the actin monomer A in the different biochemical states (AM.ADP.P_i, thinnest line; AM.ADP, medium thickness line; and AM, thickest line). Of the four structural states only M₁ is shown for clarity. The black lines are in control solution (no added P_i) and the horizontal lines show the free energy of the detached states. The green lines show the effect of the addition of 10 mm P_i on the free energy level of the AM.ADP, AM and M.ATP states (the upward shift accounting for the reduction in ΔG).