pyrimidinones and 6-carboxyfluorescein

Osmotic shrinkage changes the surface properties of dipalmitoylphosphatidylcholine large unilamellar vesicles depending on the phase state of the bilayer. In the gel state, shrinkage produces an increase in the adsorption of hydrophobic dyes, such as Merocyanine 540 (MC540) monomers, toluidine and anilinonaphthalene sulfonic acid (TNS, ANS). In the fluid state, shrinkage does not affect the bilayer surface when gradients between the inner and the outer compartments below 0.2-0.25 M NaCl (higher concentration outside) are applied. Larger differences in concentrations produce an increase in packing as inferred from the desorption of the MC monomers. Kinetic experiments show that the surface changes correlate with the volume decrease produced by the water extrusion from the vesicle interior. It is interpreted that the decrease of water content compels the vesicles to a state in which defects at the membrane surface are likely to occur when the bilayer is in the gel state.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Coloring Agents; Diphenylhexatriene; Fluoresceins; Fluorescence Polarization; Fluorescent Dyes; Gels; Kinetics; Lipid Bilayers; Liposomes; Nephelometry and Turbidimetry; Osmosis; Particle Size; Pyrimidinones; Sodium Chloride; Spectrophotometry; Surface Properties; Temperature; Water

Melittin fragments carrying spiropyran were synthesized, and their distribution in phospholipid bilayer membrane was studied by using spiropyran as a probe. Spiropyran was connected to the side chain of a Glu residue (Glu(OSp)), and the residue was replaced for the fourth position of melittin (1-7) fragment (M7Sp). M7Sp showed a high affinity for phospholipid membrane. The spiropyran group of M7Sp was converted to a merocyanin group by UV irradiation, which reduced the amount of the peptide bound to the membrane to the half of the initial amount. The location of the merocyanin group of M7Sp in the membrane was evaluated by the rate of thermal isomerization from merocyanin to spiropyran, which is sensitive to the microenvironment of merocyanin. A large fraction of the merocyanin group isomerized rapidly back to a spiropyran form, indicating that M7Sp is located in a relatively hydrophobic region of the membrane. Although the interaction of the peptide with phospholipid membrane is affected by photoisomerization of the spiropyran substituent, spiropyran was shown to be a useful tool to evaluate the location of the peptide in the lipid membrane.

Topics: Amino Acid Sequence; Benzopyrans; Chemical Phenomena; Chemistry, Physical; Fluoresceins; Fluorescent Dyes; Indoles; Isomerism; Kinetics; Melitten; Membranes, Artificial; Molecular Sequence Data; Nitro Compounds; Peptide Fragments; Phospholipids; Pyrimidinones; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Thermodynamics