Freeze-fracture studies on lipids and membranes

Freeze-fracture electron microscopy is especially useful for investigation of lipid structures by the advantageous fracture course within hydrophobic zones. Freezing is, on the other hand, a restriction because the structures of lamellar and non-lamellar phase states with disordered acyl chains (L-a lpha H-II, cubic) are difficult to preserve. An important aspect of this me thod is therefore the lipid structure of phase states with ordered acyl cha ins (crystal, gel), and with a different degree of hydration. Freeze-fractu re of pure lipid systems creates a valid representation of the structure of non-lamellar phases and of the general structure of the "lamellar" lipid b ilayer, and lamellar phases with characteristic deformations (ripples, curv atures, plane sectors) can be identified. Fracture through the hydrophobic bilayer centre of biological membranes reveals characteristic protein compo nents, the intramembraneous particles (IMPs). The lateral distribution of t he IMPs is a helpful marker for fluid and rigid phase states, also without deformation of the lamella. The overall history and the present state of kn owledge concerning the different structures revealed by the freeze-fracture and freeze-etch techniques in lipid systems, and to a limited extent in bi ological membranes, is reviewed, taking into account studies from our own l aboratory. (C) 2001 Elsevier Science Ltd. All rights reserved.