Biomedical subjects
Publications and source records attributed to S W Hui.
Electron diffraction patterns were obtained for the first time from single wet phospholipid bilayers and from wet human erythrocyte membranes by using a temperature-controlled electron microscope hydration stage. Selective area diffraction showed the existence of semicrystalline domains. A structural transition was observed at the transition temperature of the wet dipalmitoyl lecithin bilayer.
The structure of fully hydrated dipalmitoyl lecithin single bilayers, and monolayers deposited on Formvar substrates are studied by electron diffraction, using a hydration stage fitted to an electron microscope. Selective area diffraction patterns of these films indicate that there are domains consisting of mosaics of crystallites of hexagonally packed lipid chains. The size of these domains are typically several mum in diameter. The diffraction intensity agrees with that calculated from the electron scattering factor of the hydrocarbon chains of the lipid molecule.
Domains in lipid bilayers may exist when two or more phases are allowed. However, the geometry of domains are governed by additional constraints. The most direct way to study the geometry of domains is by microscopy. Electron diffraction patterns that are characteristic of particular molecular packings are used to enhance the contrast of domains by electron microscopy. Surface features associated with lipid phases are utilized in freeze-fracture electron microscopy to define domains. X-ray microanalysis helps to identify the composition of lipids in domains. Phase-specific fluorescence dyes such as merocyanine 540 (MC540) are useful in delineating domains in monolayers and bilayers. MC540 is also sensitive in detecting molecular packing stress below the onset of the bilayer-hexagonal phase transition. Domains in monolayers and bilayers, mapped by different microscopic techniques, are compared.