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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.


Molecular events and energetic processes included in the cross-bridge cycle. Arrows (a), (b), (c) and (d) denote energetic processes.
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f12-5_11: Molecular events and energetic processes included in the cross-bridge cycle. Arrows (a), (b), (c) and (d) denote energetic processes.

Mentions: In this section we analyze the energy flow included in a cross-bridge cycle. The reaction steps included in the cross-bridge cycle are classified into two groups, as shown in Figure 12. One reaction group passes inside the AM* complex and includes the following steps: (a) AM* complex formation, i.e., A+M*↔AM*, (b) generation of M*after coupled with sliding movement of the myosin head on the actin molecule, i.e., AM*before→AM*after, and (c) dissociation of AM*after, i.e. AM*after→A+M*after. The other reaction group passes outside the AM* complex and includes the following steps: (d) hydration of M*after for reformation of M*before, i.e. M*after→M*before in the surrounding medium.


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
Molecular events and energetic processes included in the cross-bridge cycle. Arrows (a), (b), (c) and (d) denote energetic processes.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f12-5_11: Molecular events and energetic processes included in the cross-bridge cycle. Arrows (a), (b), (c) and (d) denote energetic processes.
Mentions: In this section we analyze the energy flow included in a cross-bridge cycle. The reaction steps included in the cross-bridge cycle are classified into two groups, as shown in Figure 12. One reaction group passes inside the AM* complex and includes the following steps: (a) AM* complex formation, i.e., A+M*↔AM*, (b) generation of M*after coupled with sliding movement of the myosin head on the actin molecule, i.e., AM*before→AM*after, and (c) dissociation of AM*after, i.e. AM*after→A+M*after. The other reaction group passes outside the AM* complex and includes the following steps: (d) hydration of M*after for reformation of M*before, i.e. M*after→M*before in the surrounding medium.

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.