Surface-Induced X-Ray Reflection Visualization of Membrane Orientation and Fusion into Multibilayers
G. Cevc 1,
W. Fenzl 2, and
L. Sigl 2
1 Medizinische Biophysik—Forschungslaboratorium, Urologische Klinik und Poliklinik der Technischen Universität München, Klinikum rechts der Isar, Ismaningerstrasse, 22, D-8000 München 8, Federal Republic of Germany 1, E.C.
2 Sektion Physik der Ludwig-Maximilians Universität München, Geschwister Scholl-Platz 1, D-8000 München 22, Federal Republic of Germany
The fusion of lipid membranes at the air-water interface has been detected with the use of x-ray reflection as a high-resolution, surface-sensitive technique. The rate of this fusion for dimyristoylphosphatidylcholine (DMPC) bilayers is the highest at 29°C, which coincides with the chain-melting phase-transition temperature for the top membrane layers. After 6 hours of incubation a stack of at least ten surface-ordered membrane bilayers in equilibrium with the bulk vesicle suspension is formed. Such fusion is thus surface-catalyzed but not restricted to the first surface layer. The process involves partial membrane dehydration near the solution surface which decreases toward the bulk.
