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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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Schematic presentation of energy flow at the AM* complex. (A) Energy flow during sliding movement. The molecular mechanism borrows energy from the environment and converts it into gross work. (B) Energy flow after the end of the ATPase lifetime. The energy supplied by ATP hydrolysis is released into the environment as heat. The borrowed energy is covered by part of the released energy. The energy used to maintain the high-energy state of the myosin head is released as heat into the environment.
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f11-5_11: Schematic presentation of energy flow at the AM* complex. (A) Energy flow during sliding movement. The molecular mechanism borrows energy from the environment and converts it into gross work. (B) Energy flow after the end of the ATPase lifetime. The energy supplied by ATP hydrolysis is released into the environment as heat. The borrowed energy is covered by part of the released energy. The energy used to maintain the high-energy state of the myosin head is released as heat into the environment.

Mentions: The constant heat production (CHP), which corresponds to part of the energy supplied by ATP hydrolysis, is used to maintain the myosin head in the high-energy state M*. The rest of the supplied energy is equivalent to the amount of energy which the actomyosin system can borrow from the environment, and AM* complex converts the borrowed energy into gross work production, i.e., work and heat production. When the lifespan of the myosin ATPase ends, the myosin head releases the energy supplied by ATP hydrolysis into the environment as heat. An energy balance among constant heat production, gross work, and the energy supplied by ATP hydrolysis is then achieved, as shown in Figure 11A and 11B.


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
Schematic presentation of energy flow at the AM* complex. (A) Energy flow during sliding movement. The molecular mechanism borrows energy from the environment and converts it into gross work. (B) Energy flow after the end of the ATPase lifetime. The energy supplied by ATP hydrolysis is released into the environment as heat. The borrowed energy is covered by part of the released energy. The energy used to maintain the high-energy state of the myosin head is released as heat into the environment.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f11-5_11: Schematic presentation of energy flow at the AM* complex. (A) Energy flow during sliding movement. The molecular mechanism borrows energy from the environment and converts it into gross work. (B) Energy flow after the end of the ATPase lifetime. The energy supplied by ATP hydrolysis is released into the environment as heat. The borrowed energy is covered by part of the released energy. The energy used to maintain the high-energy state of the myosin head is released as heat into the environment.
Mentions: The constant heat production (CHP), which corresponds to part of the energy supplied by ATP hydrolysis, is used to maintain the myosin head in the high-energy state M*. The rest of the supplied energy is equivalent to the amount of energy which the actomyosin system can borrow from the environment, and AM* complex converts the borrowed energy into gross work production, i.e., work and heat production. When the lifespan of the myosin ATPase ends, the myosin head releases the energy supplied by ATP hydrolysis into the environment as heat. An energy balance among constant heat production, gross work, and the energy supplied by ATP hydrolysis is then achieved, as shown in Figure 11A and 11B.

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