Double-chain alkyl amphiphiles with oligo-l-glutamic acid-head group were prepared. These compounds were dispersed in water at pH 8 to 9 to form bilayer aggregates, in which helical and hollow structures were contained. New CD bands were observed in the solution.
The effect of synthetic cationic lipids on the structure of DNA was studied. The fluorescence enhancement of ethidium bromide on intercalation into DNA was suppressed by the addition of bilayer-forming lipids, but not by micellar ones. Results on the fluorescence depolarization index suggest that ethidinm bromide is not released from DNA by lipids intercalated into DNA. CD spectra of the DNA-lipid complexes revealed that the structure of DNA was changed only by bilayer-forming lipids at temperatures lower than their Tc values. Thus, the conformation of DNA is forced to change by cationic lipids forming the rigid bilayer membrane so that ethidium bromide fluorescence might be reduced, and the conformation can be controlled by selection of the appropriate lipid and temperature.Key words: Bilayer membrane; Cationic lipid; DNA conformation; Ethidium bromide Bilayer membranes formed with cationic lipids have been successfully used as DNA carriers into cultured eukaryotic cells [9][10][11][12][13]. Since these membranes have fluid two-dimensional surface cationic groups neutralizing the anionic phosphate groups of the DNA, DNA interacting with the membranes would exhibit a different conformational change from that interacting with metal ions and proteins. In this communication, we studied the effects on the conformation of DNA of synthetic cationic lipids with various properties of membrane fluidity and aggregate morphology, and show that cationic lipids forming the rigid bilayer membrane can induce a structural change in DNA and that the structure of DNA can be controlled by selection of the lipids and temperature.
Materials and methods
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