An Induced Potential Model for Myosin Head Motion along an Actin Filament in Contracting Muscle : I. Fundamental Muscle Properties

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Our previous model describing muscle contraction [J. Muscle Res. Cell Motility 9 (1988) 248-260] has been reformulated to explain existing experimental data more comprehensively. We assume here that attachment of an ATP-activated myosin head causes a local deformation of about 16 nm along the actin filament, a deformation which stabilizes the binding of the myosin head and tends to move with it; an analogous behavior to the polaron in solid state physics. In addition, another local structural change is assumed to occur close to the 16 nm deformation which induces the potential of force and causes the potential barrier against backward motion of a myosin head as discussed in our previous paper. The tension transients in quick length changes are explained well with the former assumption, whereas calculations based upon the latter assumptions show good agreement with experimental data on the force-velocity relation and energy liberation during muscle contraction and also on the motion of myosin-coated beads along actin cables for negative load in the intermodal cell of an alga. In the proposed model, the myosin head is trapped in the self-induced potential well on the actin filament and repeats step motions between actin molecules dragging the potential well while it produces tension. One attachment/detachment cycle of the head which contains many step motions corresponds to one ATPase cycle. The myosin head translates along the actin filament over about 135 nm in free shortening during one ATPase cycle. Results lead to a hypothesis as to why a myosin molecule has two heads.
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An Induced Potential Model for Myosin Head Motion along an Actin Filament in Contracting Muscle : I. Fundamental Muscle Properties

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