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Load-dependent sliding direction change of a myosin head on an actin molecule and its energetic aspects: Energy borrowing model of a cross-bridge cycle

View Article: PubMed Central - PubMed

ABSTRACT

A model of muscle contraction is proposed, assuming loose coupling between power strokes and ATP hydrolysis of a myosin head. The energy borrowing mechanism is introduced in a cross-bridge cycle that borrows energy from the environment to cover the necessary energy for enthalpy production during sliding movement. Important premises for modeling are as follows: 1) the interaction area where a myosin head slides is supposed to be on an actin molecule; 2) the actomyosin complex is assumed to generate force F(θ), which slides the myosin head M* in the interaction area; 3) the direction of the force F(θ) varies in proportion to the load P; 4) the energy supplied by ATP hydrolysis is used to retain the myosin head in the high-energy state M*, and is not used for enthalpy production; 5) the myosin head enters a hydration state and dehydration state repeatedly during the cross-bridge cycle. The dehydrated myosin head recovers its hydrated state by hydration in the surrounding medium; 6) the energy source for work and heat production liberated by the AM* complex is of external origin. On the basis of these premises, the model adequately explains the experimental results observed at various levels in muscular samples: 1) twist in actin filaments observed in shortening muscle fibers; 2) the load-velocity relationship in single muscle fiber; 3) energy balance among enthalpy production, the borrowed energy and the energy supplied by ATP hydrolysis during muscle contraction. Force F(θ) acting on the myosin head is depicted.

No MeSH data available.


Definition of interaction area and interaction unit. A radial projection of the actin filament of a half helical pitch is shown by solid blue lines. The area corresponding to an actin molecule is shown by dotted black lines, including the space between neighboring actin molecules. The interaction area on the surface of the actin molecule is represented by a shaded rhomboid. The interaction unit, consisting of four adjacent interaction areas, is framed by red lines. The actin target areas are tentatively represented by ellipsoids in the interaction area.
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f1-5_11: Definition of interaction area and interaction unit. A radial projection of the actin filament of a half helical pitch is shown by solid blue lines. The area corresponding to an actin molecule is shown by dotted black lines, including the space between neighboring actin molecules. The interaction area on the surface of the actin molecule is represented by a shaded rhomboid. The interaction unit, consisting of four adjacent interaction areas, is framed by red lines. The actin target areas are tentatively represented by ellipsoids in the interaction area.

Mentions: It is convenient to use radial projection of the actin filament12 to describe the movement of the myosin head on actin molecules, as shown in Figure 1. The interaction area on the actin molecule is shown by a shadowed rhomboid on the radial projection. Each of the interaction areas is assumed to contain the actin-targeting area and is also assumed to include part of the adjacent actin molecule. In addition, an interaction unit is defined as a region on the actin filament composed of four adjacent interaction areas along the right-handed long-pitch actin strand.


Load-dependent sliding direction change of a myosin head on an actin molecule and its energetic aspects: Energy borrowing model of a cross-bridge cycle
Definition of interaction area and interaction unit. A radial projection of the actin filament of a half helical pitch is shown by solid blue lines. The area corresponding to an actin molecule is shown by dotted black lines, including the space between neighboring actin molecules. The interaction area on the surface of the actin molecule is represented by a shaded rhomboid. The interaction unit, consisting of four adjacent interaction areas, is framed by red lines. The actin target areas are tentatively represented by ellipsoids in the interaction area.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f1-5_11: Definition of interaction area and interaction unit. A radial projection of the actin filament of a half helical pitch is shown by solid blue lines. The area corresponding to an actin molecule is shown by dotted black lines, including the space between neighboring actin molecules. The interaction area on the surface of the actin molecule is represented by a shaded rhomboid. The interaction unit, consisting of four adjacent interaction areas, is framed by red lines. The actin target areas are tentatively represented by ellipsoids in the interaction area.
Mentions: It is convenient to use radial projection of the actin filament12 to describe the movement of the myosin head on actin molecules, as shown in Figure 1. The interaction area on the actin molecule is shown by a shadowed rhomboid on the radial projection. Each of the interaction areas is assumed to contain the actin-targeting area and is also assumed to include part of the adjacent actin molecule. In addition, an interaction unit is defined as a region on the actin filament composed of four adjacent interaction areas along the right-handed long-pitch actin strand.

View Article: PubMed Central - PubMed

ABSTRACT

A model of muscle contraction is proposed, assuming loose coupling between power strokes and ATP hydrolysis of a myosin head. The energy borrowing mechanism is introduced in a cross-bridge cycle that borrows energy from the environment to cover the necessary energy for enthalpy production during sliding movement. Important premises for modeling are as follows: 1) the interaction area where a myosin head slides is supposed to be on an actin molecule; 2) the actomyosin complex is assumed to generate force F(θ), which slides the myosin head M* in the interaction area; 3) the direction of the force F(θ) varies in proportion to the load P; 4) the energy supplied by ATP hydrolysis is used to retain the myosin head in the high-energy state M*, and is not used for enthalpy production; 5) the myosin head enters a hydration state and dehydration state repeatedly during the cross-bridge cycle. The dehydrated myosin head recovers its hydrated state by hydration in the surrounding medium; 6) the energy source for work and heat production liberated by the AM* complex is of external origin. On the basis of these premises, the model adequately explains the experimental results observed at various levels in muscular samples: 1) twist in actin filaments observed in shortening muscle fibers; 2) the load-velocity relationship in single muscle fiber; 3) energy balance among enthalpy production, the borrowed energy and the energy supplied by ATP hydrolysis during muscle contraction. Force F(θ) acting on the myosin head is depicted.

No MeSH data available.