| Budget Amount *help |
¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1987: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1986: ¥700,000 (Direct Cost: ¥700,000)
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| Research Abstract |
Actin filaments are identified ubiquitously in the periphery of non-muscle cell as well as in muscle cell, taking various assembly structures such as the isotropic structure and the bundle form in a crystalline-like structure or in a liquid-crystalline structure. The individual structures are changeable in response to the external stimulations, and the change may play important roles in the cellular functions. We have studied how the assembly structures of the actin filaments change in response to the imbalance of osmolarity which has made by: 1. the use of osmometer, 2. the addition of poly(ethylene glycol)s of high molecular weights.
The results obtained by method 1 are: (1) The actin filaments are compressed clastically in response to the osmotic stress resulting from the imbalance of the osmolarity. The compression increases the free energy of the filament and also decreases the flow of water along the imbalance of the osmolarity (volume flow). (2) An increase in the concentration o
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f the actin filament causes a phase transition from the isotropic fluid phase (sol phase) to the isotropic solid phase (gel phase) above 7 mg/ml (glassy transition), and the volume flow is completely eliminated in the gel phase. (3) Shortening the filament length by a specific actin binding protein, gelsolin, increases the critical concentration for the glassy transition. (4) If the filament solution in the isotropic phase is subjected to the osmotic stress larger than a critical intensity, it takes a transition to the anisoropic phase in which the filaments should be in bundle form, and a large volume flow follows the transition. (5) ABP which can crosslink the actin filaments increases the stability of the isotropic phase against the osmotic stress.
The results obtained by the method 2 are: (1) Above a criticl intensity of the PEG-induced osmotic stress, the isotropicaly distributed actin filaments make a bundle in a crystalline-like structure and an abrupt increase in the light scattering follows it. (2) The finding in (1) enabled us to make a quantitative phase diagram of the actin filament solutions which is represented by the two parameters, i.e., the interaction energy between the filaments and the volume fraction. Less
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