生物試料の保存における糖の役割
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概要
- 論文の詳細を見る
Organisms that survive extreme dehydration often contain large quantities of soluble sugars, in particular di- and oligosaccharides. The presence of these sugars is believed to be one of the adaptations that allows dehydration tolerant organisms, including many plant seeds, to survive the loss of most of their cellular water. Cellular membranes are especially sensitive to the effects of dehydration. Sugars can exert various effects on membranes and may help preserve their structural and functional stability during dehydration. This review will describe the physical effects of dehydration on phospholipid bilayers and will explain how sugars can modify these effects to help stabilize membranes. As water is removed from between membranes, the close approach of the bilayers leads to physical stresses in the membranes. These stresses cause membrane lipids to be compressed together. During the fluid-to-gel phase transition, phospholipids move closer together and decrease the average surface area per lipid molecule. Thus, the dehydration-induced compression in the membranes may result in the phospholipids' transition from the fluid to the gel phase. Sugars that remain between membranes as water is removed can limit the close approach of the bilayers and, thus, can decrease the compressive physical stress that causes the fluid-to-gel phase transition to occur during dehydration. Therefore, in the presence of interlamellar sugars, the fluid-to-gel phase transition temperature (T_m) of a dry phospholipid does not increase as much as it does in the absence of sugars. Vitrification of the interlamellar sugar solution has the additional effect of adding a mechanical resistance that hinders the lateral movement of phospholipids within the bilayer and makes it necessary to cool the lipids to a lower temperature to bring about the transition to the gel phase. Thus, when the sugar solution vitrifies between fluid phase bilayers, T_m is depressed below its fully hydrated value (T_O). Neither of these effects of sugars on phospholipid phase transitions depends upon specific interactions between the sugars and lipids; instead, they can he explained using simple thermodynamics.
- 低温生物工学会の論文
- 2001-07-30