Alfar Nicksch

X-ray analysis and calorimetry on phosphatidylcholine model membranes. The influence of length and position of acyl chains upon structure and phase behaviour

The effect of variation of the acyl chain composition of phosphatidylcholines upon thermal behaviour of multilamellar liposomes was evaluated by calorimetry and X-ray studies. A total of thirteen different phosphatidylcholines were examined. They differed from each other in the length as well as in the position of the acyl chains in the glycerol backbone. The experimental results show that the hitherto accepted phase scheme for phosphatidylcholine-water systems is incomplete and has to be extended to include the behaviour of samples that have been stored for long times at low temperatures. The X-ray results show that the structure of the new low-temperature phase is not in agreement with the hexagonal packing of the acyl chains. To explain the X-ray results, a two-dimensional orthorhombic unit cell has to be assumed in order to fit all the observed reflexes in the wide-angle region.

The synthesis of phospholipids by direct amination

Abstract The bromoethylesters of phosphatidic acids and their analogues are general intermediates in the synthesis of phospholipids. A direct amination with different amines such as ammonia, methylamine, dimethylamine and trimethylamine results in the corresponding phosphatidylethanolamines and -cholines. In addition to the well elaborated reactions of bromoethylesters with trimethylamine and dimethylamine, the synthesis of phosphatidylethanolamines and -( N -methyl)-ethanolamines by amination with ammonia and methylamine is now possible in high yields (> 90%) without the need of the usual protecting groups.

Use of energy transfer to assay the asseciation of proteins with lipid membranes

Abstract A method is described for the rapid and quantitative assay of the association of proteins with lipid membranes. The method utilizes the nonradiative transfer of energy between fluorescent groups in the protein and fluorescent groups attached to the polar heads of the lipids in the membrane. The association constant for the electrostatic association of trypsin with bilayers of the negatively charged lipid, 1,2-dimyristoyl- sn -glycerol-3-phosphoric acid methyl ester (MPA) at a salt concentration of 5 m m and pH 8 was found to be (2.32 ± 0.07) × 10 5 m −1 . The stoichiometry of lipid to protein in the association complex is 40–50 lipid molecules per trypsin molecule. Honey-bee venom melittin and the serum apolipoprotein, apo-Lp-Ala, were shown to associate with lecithin vesicles. Acetylcholine esterase isolated from the electric organ of the electric eel according to the method of Leuzinger and Baker [(1967) Proc. Nat. Acad. Sci. USA 57, 446–451] was shown to be incapable of associating with lecithin or MPA bilayers.