The Use of Freeze-Fracture and Freeze-Etching Electron Microscopy for Phase Analysis and Structure Determination of Lipid Systems

Abstract

Recent improvements including the development of novel ultra-rapid cryofixation procedures and the use of high resolution shadowing techniques suggest that freeze-etching electron microscopy may be particularly useful for studying phase diagrams and the structure of individual phases in lipid containing systems. Use of the freeze-etching technique, however, requires careful evaluation of the effects of cryofixation, fracture and etching upon the sample structure. The combined use of X-ray diffraction before and low temperature X-ray diffraction after freezing prior to fracture, etching and replication of samples whose structures are known provides a sensitive assessment of the effects of cryofixation upon lipid phases. Investigation of a number of different lipid phases by the combined use of x-ray diffraction, low temperature X-ray diffraction and freeze-etching electron microscopy revealed the cryofixation procedures best adapted for studying each lipid phase and led to a better understanding of the cryofixation methods. We discuss here the results obtained by using this combined X-ray diffraction — freezeetching approach and describe in more detail the most recent data on the structure of lipid-water cubic phases.