20 ミナミウシノシタ防御物質の脂質二重膜透過性昂進機構(口頭発表の部)
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概要
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Soles of the genus Pardachirus are characterized by their chemical defense against predation with a copious and ichthyotoxic secretion being discharged upon disturbance. Two chemical classes of bioactive entities, namely, steroid monoglycosides and amphiphilic peptides, have been isolated from each secretion of two different biological species. Based on permeabilization of phospholipid bilayer exhibited by these components at the lower concentrations than their EC's for various bioactivity, their mechanisms of action may well be attributed to nonspecific derangement of animal cell membrane without binding to any particular biomolecule. In this study, an assay method of membrane permeabilization was employed, where calcein was encapsulated in unilamellar liposomes of egg-yolk phosphatidylcholine as the cellular model and its leakage outward was assessed by the increase of fluorescence, in order to evaluate (i) the function of the hydrophobic N-terminal region of pardaxin M-1, a representative peptidic component, as the membrane binding region, and (ii) the significance of the existence in the defense secretion of steroid glycosides, i.e., pavoninins and mosesins, which appear to behave in a similar manner as pardaxins in this membranal action but with lower potencies. As a result of the binding analyses with concentrations of the test sample and liposomes as two independent variants and application of Langmuir's adsorption isotherm with the two-state model to the outcomes, the N-terminal region was revealed not only to function as the strong binding region, but also to enhance when bound the deranging activity putatively of the α-helical region at the middle of the 33 amino acid sequence by the factor of 6 times. In this model assay with varied cholesterol contents in the lipid bilayer, the defensive steroid glycosides were shown to be indifferent to this membranal component in their permeabilizing action, being unlike the conventional hemolytic saponins. In addition, different kinetics exhibited here between the steroid glycosides and pardaxins implied that the former's is rather transient while the latter's is persistent with all-or-none rupture of liposomes. An extent of synergism, possibly with such differently allotted functions in the defensive action, was also shown between the two chemical entities.
- 天然有機化合物討論会の論文
- 1994-09-20
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