Phosphatidic acid distribution on the external surface of mixed vesicles

Abstract

A new method has been developed to detect the distribution of phosphatidic acid on the external surface of mixed phospholipid vesicles. Some positive dyes undergo large absorbance changes when the spatial separation between two or more dye molecules is smaller than a critical distance. When these dyes interact with mixed phospholipid vesicles, the absorbance changes may be utilized to calculate the amount of phosphatidic acid molecules which, on the external surface, occupy nearby positions not exceeding the critical dye distance, i.e., the amount of paired phosphatidic acid molecules. This amount was found to be higher than that calculated by statistical methods, indicating that phosphatidic acid molecules tend to be associated, in spite of the electrostatic repulsion between negative groups. The dependence of the amount of paired phosphatidic acid molecules on the pH, phosphatidylcholine:phosphatidic acid ratio, and temperature has been also analyzed.

Phosphatidic acid affects structural organization of phosphatidylcholine liposomes. A study of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-trimethylammonium-phenyl)-6-phenyl,1,3,5-hexatriene (TMA-DPH) fluorescence decay using distributional analysis

“…The small cross-section of the phosphate group cannot tightly cover the layer surface [9], so that water molecules have to be accommodated as spacer molecules into the polar headgroup region [11]. It was suggested that, in a biological membrane, PA forms hydrogen bonded dimers [30] or strands [11]. On the other hand, the hydrogen bonding PA packs more closely than PC in a monolayer [9].…”

Surface potential of lipid membrane estimated from the partitioning of methylene blue into liposomes

“…This group of dyes undergoes dimerization in aqueous solution at concentrations greater than 10~4 M. The stacking interactions give not only dimers but also «-meric forms (Ghosh & Mukerjee, 1970). However, the extinction coefficients of dimer and «-meric form at the maximum absorbance of the longer wavelength band (664 nm) are almost the same (Massari & Pascolini, 1977;Vitagliano et al, 1973). Therefore, an n-mer is considered to be equivalent to «/2 dimers.…”

“…where n0 and «d are moles of the MB molecules in total and in dimeric form (gram equivalent of dimers), respectively, VB is the volume of the buffer solution containing MB, the volume of membrane phase, VM, is very small to be neglected in eq 1, and 6m and ed are the extinction coefficients of monomer and dimer, respectively. ed in bulk and in membrane is considered to be almost the same (Massari & Pascolini, 1977). This will be discussed later in detail.…”

Bolaform surfactants with polyoxometalate head groups and their assembly into ultra-small monolayer membrane vesicles

“…3a). As an independent experiment, the metachromatic effect of methylene blue was used as a sensitive probe for the symmetry or asymmetry of MLMs112728. As no blue shift of the absorption band was detected (data given in Supplementary Fig.…”