生体膜のトポグラフィー解析の新手法
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概要
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It is very important to make available methods for the study of molecules within biomembranes : this is necessary in particular to define the topography of membrane-bound proteins, sterols, ubiquinones, carotenoids, etc Khorana, Breslow and others have tried to use, for this goal, probes consisting of a phospholipid or an amphiphile bearing a photosensitive group, in the hope that irradiation of membranes containing them would lead to labelling at a definite level inside the bilayer ; their results have been uniformly disappointing, as the labelling is not at all specific, due to the extensive disorder of the phospholipidic matrix.<BR>We have conceived and synthesized a novel type of transmembrane probe 1a, which is shown by <SUP>2</SUP>H NMR and DSC studies to possess favourable physico-chemical properties for membrane topographical studies. It was also shown to be remarkably selective for attack of membrane components near the middle of the bilayer, due to its transbilayer construction and to the concomitant use of cholesterol to improve the order of the lipid chains of the membrane : the myristoyl chains functionalized at C-11, 12 and 13 positions covered 95% of total photolabelled myristates, and cholesterol was principally functionalized at the C-25 position on the side-chain. This indicates the formation of a highly ordered bilayer structure and proved directly the perpendicular orientation of cholesterol to the membrane plane with its chain terminal buried in the middle of the membrane. However, it remained necessary to check whether the addition of cholesterol, a normal constituent of biomembranes, would not, by itself, improve the selectivity of “half-probes” similar to those of Khorana and of Breslow. This is in-deed the case. The new photolabelling systems described here should be useful for the study of the topography of proteins and other constituents in membranes.
- 社団法人 有機合成化学協会の論文
- 1995-09-01