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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.


Related in: MedlinePlus

Relationships among gross work production, sliding velocities, and molecular behavior of myosin head on actin molecules. Note that constant heat production is omitted. The black solid line represents gross work Wg(θ). The blue line denotes work production W(θ). The red line shows heat production H(θ), defined by Wg(θ)−W(θ). The relationship between the number of actin molecules on which a myosin head slides during τ and the sliding velocity is shown at the top. Velocity 0.076 Vmax at which Vp(θ)=0 is shown by the red arrow.
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f14-5_11: Relationships among gross work production, sliding velocities, and molecular behavior of myosin head on actin molecules. Note that constant heat production is omitted. The black solid line represents gross work Wg(θ). The blue line denotes work production W(θ). The red line shows heat production H(θ), defined by Wg(θ)−W(θ). The relationship between the number of actin molecules on which a myosin head slides during τ and the sliding velocity is shown at the top. Velocity 0.076 Vmax at which Vp(θ)=0 is shown by the red arrow.

Mentions: Relationships among sliding velocities, energetic quantities and the molecular behaviors of a myosin head are summarized in Figure 14. The number of actin molecules on which the myosin head slides during duration τ and characteristic movements of the myosin head around the actin filament are indicated.


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
Relationships among gross work production, sliding velocities, and molecular behavior of myosin head on actin molecules. Note that constant heat production is omitted. The black solid line represents gross work Wg(θ). The blue line denotes work production W(θ). The red line shows heat production H(θ), defined by Wg(θ)−W(θ). The relationship between the number of actin molecules on which a myosin head slides during τ and the sliding velocity is shown at the top. Velocity 0.076 Vmax at which Vp(θ)=0 is shown by the red arrow.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC5036636&req=5

f14-5_11: Relationships among gross work production, sliding velocities, and molecular behavior of myosin head on actin molecules. Note that constant heat production is omitted. The black solid line represents gross work Wg(θ). The blue line denotes work production W(θ). The red line shows heat production H(θ), defined by Wg(θ)−W(θ). The relationship between the number of actin molecules on which a myosin head slides during τ and the sliding velocity is shown at the top. Velocity 0.076 Vmax at which Vp(θ)=0 is shown by the red arrow.
Mentions: Relationships among sliding velocities, energetic quantities and the molecular behaviors of a myosin head are summarized in Figure 14. The number of actin molecules on which the myosin head slides during duration τ and characteristic movements of the myosin head around the actin filament are indicated.

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