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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

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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.


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Twists and buckling of actin filaments observed in vitro. (A) Right-handed super-coiled actin filament. (B) Buckled actin filament. (C) Left-handed super-coiled actin filament. PE and BE represent the pointed and barbed ends of the actin filament, respectively. The pointed end of the actin filament is sticks by chance to a glass surface or is attached to the glass surface as illustrated.
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f2-5_11: Twists and buckling of actin filaments observed in vitro. (A) Right-handed super-coiled actin filament. (B) Buckled actin filament. (C) Left-handed super-coiled actin filament. PE and BE represent the pointed and barbed ends of the actin filament, respectively. The pointed end of the actin filament is sticks by chance to a glass surface or is attached to the glass surface as illustrated.

Mentions: Twists in actin filaments sliding on a myosin-coated glass surface7 or on a myosin track8 have been reported. When the pointed end of an actin filament was stuck on the surface, Tanaka et al. observed a right-handed super-coil of the actin filament (Fig. 2A), buckling of the actin filament (Fig. 2B) or a left-handed super-coil of the actin filament (Fig. 2C), while Nishizaka et al. most frequently observed a left-handed super-coil of the actin filament on the myosin track (Fig. 2C). In the case of the myosin track, the pointed end of the actin filament was attached to the glass surface. These results suggest that the force acting at a cross-bridge contains a torque component around the axis of the actin filament and that the direction of the force acting on the myosin head varies depending on conditions.


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
Twists and buckling of actin filaments observed in vitro. (A) Right-handed super-coiled actin filament. (B) Buckled actin filament. (C) Left-handed super-coiled actin filament. PE and BE represent the pointed and barbed ends of the actin filament, respectively. The pointed end of the actin filament is sticks by chance to a glass surface or is attached to the glass surface as illustrated.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f2-5_11: Twists and buckling of actin filaments observed in vitro. (A) Right-handed super-coiled actin filament. (B) Buckled actin filament. (C) Left-handed super-coiled actin filament. PE and BE represent the pointed and barbed ends of the actin filament, respectively. The pointed end of the actin filament is sticks by chance to a glass surface or is attached to the glass surface as illustrated.
Mentions: Twists in actin filaments sliding on a myosin-coated glass surface7 or on a myosin track8 have been reported. When the pointed end of an actin filament was stuck on the surface, Tanaka et al. observed a right-handed super-coil of the actin filament (Fig. 2A), buckling of the actin filament (Fig. 2B) or a left-handed super-coil of the actin filament (Fig. 2C), while Nishizaka et al. most frequently observed a left-handed super-coil of the actin filament on the myosin track (Fig. 2C). In the case of the myosin track, the pointed end of the actin filament was attached to the glass surface. These results suggest that the force acting at a cross-bridge contains a torque component around the axis of the actin filament and that the direction of the force acting on the myosin head varies depending on conditions.

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.


Related in: MedlinePlus