ELECTRON MICROSCOPE AND X-RAY DIFFRACTION STUDIES ON A HOMOLOGOUS SERIES OF SATURATED PHOSPHATIDYLCHOLINES

Three homologous saturated phosphatidylcholines were studied by electron microscopy after tricomplex fixation. The results are compared with those obtained by x-ray diffraction analysis of the same and some other homologous compounds, in the dry crystalline state and after tricomplex fixation. By electron microscopy alternating dark and light bands are observed which are likely to correspond to phosphatide double layers. X-Ray diffraction reveals the presence of lamellar structures of regular spacing. The layer spacings obtained by both methods are in good agreement. From the electron micrographs the width of the polar parts of the double layers can be derived directly. The width of the carboxylglycerylphosphorylcholine moiety of the layers is found by extrapolating the x-ray diffraction data to zero chain length of the fatty acids. When from this width the contribution of the carboxylglyceryl part of the molecules is subtracted, again we find good agreement with the electron microscope measurements. An attempt has been made to account for the different layer spacings measured in terms of orientation of the molecules within the double layers.     

The fusion of abnormal plasma lipoprotein (LP-X) and the erythrocyte membrane in patients with cholestasis studied by electronmicroscopy.

Adhesion followed by fusion of LP-X vesicles with the erythrocyte membrane is an important contribution to the erythrocyte enlargement in patients with intra or extra hepatic cholestasis. Adhesion of LP-X vesicles is demonstrated by thin section and freeze-etch electronmicroscopy. Fusion of LP-X with the erythrocyte membrane is deduced from biochemical data and freeze-etch electronmicroscopy in that the uptake of cholesterol and lecithin coincides with the increase in smooth areas on the fracture faces of the erythrocyte membrane.     

The influence of pH, Ca and protein on the thermotropic behaviour of the negatively charged phospholipid, phosphatidylglycerol

It is demonstrated that the transition temperature from the liquid-crystalline to gel state of a synthetic phosphatidylglycerol is influenced by pH, Ca²⁺ and A₁ basic protein from myelin.     

Polymorphic phase behaviour of cardiolipin as detected by 31P NMR and freeze-fracture techniques. Effects of calcium, dibucaine and chlorpromazine.

1. The influence of Ca2+ on the polymorphic phase behaviour of cardiolipin has been investigated employing 31P NMR and freeze-fracture techniques. The close correlation between the results obtained here and previous X-ray studies (Rand, R.P. and Sengupta, S. (1972) Biochim. Biophys. Acta 255, 484--492) confirms 31P NMR as a useful analytical procedure for investigating the polymorphic phase behaviour of hydrated phospholipids. 2. Ca2+ induces formation of the hexagonal (H11) phase via an intermediary phase which is observed at Ca2+/cardiolipin ratios of less than 1 (mol/mol). This intermediary appears to consist of "inverted' structure which lies adjacent to regions of bilayer structure. 3. The local anaesthetics dibucaine and chlorpromazine produce similar phase changes for cardiolipin as does Ca2+. It is suggested that the anaesthetics interact with the membrane in their charged form and induce their effects by charge neutralization.     

Intramembranous particles and chlorophyll complexes in chloroplasts.

The size and population density of large and small particles from freeze-fractured chloroplasts of three wild-type algae and of normal spinach were determined. Computer analyses of low-temperature absorption spectra of chloroplast preparations from these species were performed, and a possible correlation between the occurrence of seven chlorophyll complexes and the aforementioned properties of the intramembranous particles was studies. It was found that only single-sized particles occur in a species containing neither chlorophyll b nor chlorophyll a-685 complexes. The three remaining species carry particles of two sizes, termed large and small particles. However, from quantitative considerations it is concluded that the chlorophyll content of none of the various pigment complexes is related to the size and the population density of the studied particles. If such a relationship exists, it seems likely to be due to the carrier moiety of the chorophyll b-chlorophyll a-685 complex.