PMC

CD measurements of melittin titration by SUVs (squares) and LUVs (triangles). Due to packing distortions, SUVs have higher apparent affinity for many peptides, including melittin (see Ladokhin et al. and text for more)

Optical densities as a function of wavelength for suspensions of LUVs (solid lines) and SUVs (dashed lines). Optical densities of POPC vesicles at lipid concentrations of 0.25, 3 and 7 mM were determined using a Jasco-720 spectropolarimeter (see text)

CD measurements of Annexin B12 in solution (solid line) and when bound to LUVs (dotted line) via a Ca²⁺-dependent interfacial mechanism. Because no conformational rearrangement is expected, the coinciding spectra confirm the absence of specific artifacts due to differential scattering by LUVs when a chiral object is placed on the scattering object

Schematic representation of the two-cuvette experimental scheme for studying the influence on CD spectra of peptides of light scattering caused by LUVs. Drawing is not to scale. A standard solution of melittin in methanol was placed in cell 1, while LUV suspensions of different concentrations were placed in cell 2. The results presented here did not depend on whether cell 1 or cell 2 was closer to the light source

Calculated CD spectra for melittin completely bound to POPC LUVs and SUVs. The spectra were reconstructed from the measurements in the presence of 5 mM lipid, as described in “”. The two spectra gave identical molar ellipticity values of [Θ] = −23,700 deg cm² dmol⁻¹, corresponding to approximately 70% peptide helicity

CD spectra of melittin in methanol (40 μM, cell 1) recorded in the two-cuvette experiment shown in Fig. . a Cell 2 containing SUV suspensions at concentrations up to 7 mM. Undistorted CD spectra of melittin with up to 7 mM SUVs can be obtained for the spectral region above 200 nm. b Cell 2 containing LUV suspensions at concentrations up to 7 mM. Undistorted CD spectra of melittin can be obtained with up to 5 mM LUVs for the spectral region above 200 nm and with up to 7 mM for the spectral region above 215 nm (see values of molar ellipticity in Table )

CD spectra of the nonbinding peptide Ac-Y(AEAAKA)₄F-NH₂ (40 μM) in the presence of vesicles. a CD spectra obtained with the peptide in the same cuvette as the lipid. b CD spectra of an aqueous solution of Ac-Y(AEAAKA)₄F-NH₂ in cell 1 measured in the presence of increasing concentrations of LUVs in cell 2 (see values of molar ellipticity in Table ). The spectra are virtually identical to the spectra of (a). This validates the use of the two-cuvette experiment for studying the influence of light scattering on CD spectra obtained from solutions containing unilamellar vesicles of any size