Electron crystal structure analysis of biomembrane lipids

Because of the well-known sample crystallization difficulties which often hinder the X-ray crystal structure analysis of many long-chain lipids, Parsons and Nyburg were the first to attempt the crystallographic elucidation of a phospholipid structure using electron diffraction intensity data from more readily-available microcrystals. Subsequent electron diffraction studies of various lipids in this laboratory over the past decade have revealed a number of peculiar features of such data-particularly if these are expected to resemble X-ray data. These observations have led to a physically reasonable overview of the problem based on well-established diffraction theory and have permitted the derivation of useful analytical procedures for electron crystal structure determination. It is interesting to note that the appropriate procedure is dependent on the method used for specimen crystallization.Lipid crystals grown from solution are typically plate-like with long alkyl chains packing with axes more or less perpendicular to the best developed crystal face ; an incident electron beam thus parallels the longest unit cell axis.