EFFECT OF LIPID MOLECULES ON TWISTING MOTIONS OF DNA HELIX STUDIED BYFLUORESCENCE POLARIZATION ANISOTROPY

Time-resolved fluorescence polarization anisotropy (FPA) of two dyes ( acridine orange and ethidium bromide) intercalated in a raw DNA and a navel DNA-lipid complex has been measured on nanosecond timescale to e valuate the effect of lipid molecules on the twisting motions of DNA h elix. Steady-state fluorescence spectra show that intercalated dyes ar e not influenced much by solvents compared with free dyes, suggesting the similar microscopic environments of intercalated chromophores. The FPA decay times of both dyes are about twice larger in the DNA-lipid complex than in the raw DNA, which indicates that the lipid molecules around the helix make the twisting motion slower. The FPA decay profil es fit very well with double-exponential functions having time constan ts differing much with each other, suggesting that there exists slow a nd quick elements in the twisting motions.