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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.


Sliding traces of a myosin head in interaction areas and expressions of sliding length on the interaction unit. Black arrows represent the sliding movement of the myosin head in each interaction area, and green arrows denote Brownian movement to change the interaction area. The broken line which starts from point O shows the sliding trace of the myosin head on the interaction unit defined by the summation of each vector component representing the sliding movement of the myosin head in each interaction area. Definitions of the shortening distance Ls and the sliding distance on interaction unit Lu are shown (See text).
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f5-5_11: Sliding traces of a myosin head in interaction areas and expressions of sliding length on the interaction unit. Black arrows represent the sliding movement of the myosin head in each interaction area, and green arrows denote Brownian movement to change the interaction area. The broken line which starts from point O shows the sliding trace of the myosin head on the interaction unit defined by the summation of each vector component representing the sliding movement of the myosin head in each interaction area. Definitions of the shortening distance Ls and the sliding distance on interaction unit Lu are shown (See text).

Mentions: As a result of the sliding movement of a myosin head in several interaction areas under the given load P, a set of sliding traces of the myosin head is obtained in interaction areas. An example is shown in Figure 5. Black arrows represent the movement of the myosin head in each interaction area, and green arrows represent Brownian movement of the myosin head during the exchange process of a partner actin molecule. For simple presentation, we use the interaction unit, which is defined as four adjacent interaction areas. A trace of movement of the myosin head on the interaction unit driven by force F(θ) is represented by a long broken line given by the summation of vector components representing the sliding movements (Fig. 5). In order to derive shortening length Ls, we suppose the trace of the myosin head that is assumed to start at the original point O and finishes at point X. We define point S, which gives the intersection point of segment OX or that of an extension of segment OX with the right-side edge of the interaction unit. Then, the length of segment OS gives the sliding distance Lu of the myosin head on the interaction unit and the projection length of segment OS onto the L-axis gives the shortening length Ls of the myosin head along the axis of the actin filament during sliding movement on the inter-action unit (Fig. 5). The shortening length Ls is given as follows:


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
Sliding traces of a myosin head in interaction areas and expressions of sliding length on the interaction unit. Black arrows represent the sliding movement of the myosin head in each interaction area, and green arrows denote Brownian movement to change the interaction area. The broken line which starts from point O shows the sliding trace of the myosin head on the interaction unit defined by the summation of each vector component representing the sliding movement of the myosin head in each interaction area. Definitions of the shortening distance Ls and the sliding distance on interaction unit Lu are shown (See text).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f5-5_11: Sliding traces of a myosin head in interaction areas and expressions of sliding length on the interaction unit. Black arrows represent the sliding movement of the myosin head in each interaction area, and green arrows denote Brownian movement to change the interaction area. The broken line which starts from point O shows the sliding trace of the myosin head on the interaction unit defined by the summation of each vector component representing the sliding movement of the myosin head in each interaction area. Definitions of the shortening distance Ls and the sliding distance on interaction unit Lu are shown (See text).
Mentions: As a result of the sliding movement of a myosin head in several interaction areas under the given load P, a set of sliding traces of the myosin head is obtained in interaction areas. An example is shown in Figure 5. Black arrows represent the movement of the myosin head in each interaction area, and green arrows represent Brownian movement of the myosin head during the exchange process of a partner actin molecule. For simple presentation, we use the interaction unit, which is defined as four adjacent interaction areas. A trace of movement of the myosin head on the interaction unit driven by force F(θ) is represented by a long broken line given by the summation of vector components representing the sliding movements (Fig. 5). In order to derive shortening length Ls, we suppose the trace of the myosin head that is assumed to start at the original point O and finishes at point X. We define point S, which gives the intersection point of segment OX or that of an extension of segment OX with the right-side edge of the interaction unit. Then, the length of segment OS gives the sliding distance Lu of the myosin head on the interaction unit and the projection length of segment OS onto the L-axis gives the shortening length Ls of the myosin head along the axis of the actin filament during sliding movement on the inter-action unit (Fig. 5). The shortening length Ls is given as follows:

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.