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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.


Two components of sliding velocity Vu(θ) on the interaction unit. Vp(θ) decreases with the increase of the load, while Vn(θ) is independent of the load change. Vp(θ) vanishes around the shortening velocity V(θ)=0.076 Vmax when the sliding direction of the myosin head becomes perpendicular to the direction of the groove of actin strands, i.e., the direction of Vn(θ). Note that Vp(θ) takes the opposite direction with further load increase.
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f7-5_11: Two components of sliding velocity Vu(θ) on the interaction unit. Vp(θ) decreases with the increase of the load, while Vn(θ) is independent of the load change. Vp(θ) vanishes around the shortening velocity V(θ)=0.076 Vmax when the sliding direction of the myosin head becomes perpendicular to the direction of the groove of actin strands, i.e., the direction of Vn(θ). Note that Vp(θ) takes the opposite direction with further load increase.

Mentions: As shown in Figure 7, velocity vector Vu(θ) of the myosin head on the interaction unit is decomposed into two orthogonal vectors, Vp(θ) and Vn(θ), which are parallel and perpendicular to the direction of the groove between the right-handed long-pitch strands of the actin filament, respectively. It should be noted that the velocity component Vp(θ) vanishes when Vu(θ) becomes equal to Vn(θ) with an increase of load P, while the velocity component Vn(θ) is constant and independent of the load. This model indicates that the myosin head has two components of sliding velocity, Vp(θ) and Vn(θ), on the surface of the actin molecule, and that component Vp(θ) varies its magnitude and direction with the increase of the load while component Vn(θ) is independent of the load.


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
Two components of sliding velocity Vu(θ) on the interaction unit. Vp(θ) decreases with the increase of the load, while Vn(θ) is independent of the load change. Vp(θ) vanishes around the shortening velocity V(θ)=0.076 Vmax when the sliding direction of the myosin head becomes perpendicular to the direction of the groove of actin strands, i.e., the direction of Vn(θ). Note that Vp(θ) takes the opposite direction with further load increase.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f7-5_11: Two components of sliding velocity Vu(θ) on the interaction unit. Vp(θ) decreases with the increase of the load, while Vn(θ) is independent of the load change. Vp(θ) vanishes around the shortening velocity V(θ)=0.076 Vmax when the sliding direction of the myosin head becomes perpendicular to the direction of the groove of actin strands, i.e., the direction of Vn(θ). Note that Vp(θ) takes the opposite direction with further load increase.
Mentions: As shown in Figure 7, velocity vector Vu(θ) of the myosin head on the interaction unit is decomposed into two orthogonal vectors, Vp(θ) and Vn(θ), which are parallel and perpendicular to the direction of the groove between the right-handed long-pitch strands of the actin filament, respectively. It should be noted that the velocity component Vp(θ) vanishes when Vu(θ) becomes equal to Vn(θ) with an increase of load P, while the velocity component Vn(θ) is constant and independent of the load. This model indicates that the myosin head has two components of sliding velocity, Vp(θ) and Vn(θ), on the surface of the actin molecule, and that component Vp(θ) varies its magnitude and direction with the increase of the load while component Vn(θ) is independent of the load.

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.