title: Fracture faces of frozen membranes: 50th anniversary.
abstract: In 1961, the development of an improved freeze-etching (FE) procedure to prepare rapidly frozen biological cells or tissues for electron microscopy raised two important questions. How does a frozen cell membrane fracture? What do the extensive face views of the cell's membranes exposed by the fracture process of FE tell us about the overall structure of biological membranes? I discovered that all frozen membranes tend to split along weakly bonded lipid bilayers. Consequently, the fracture process exposes internal membrane faces rather than either of the membrane's two external surfaces. During etching, when ice is allowed to sublime after fracturing, limited regions of the actual membrane surfaces are revealed. Examination of the fractured faces and etched surfaces provided strong evidence that biological membranes are organized as lipid bilayers with some proteins on the surface and other proteins extending through the bilayer. Membrane splitting made it possible for electron microscopy to show the relative proportion of a membrane's area that exists in either of these two organizational modes.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138 dbranton@harvard.edu.
authors.forename: Daniel
authors.initials: D
authors.lastname: Branton
mesh_terms: D002462:Cell Membrane / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy / Q000266:history*; D049673:History, 20th Century; D008565:Membrane Proteins / Q000648:ultrastructure; D019697:Onions / Q000648:ultrastructure; D018517:Plant Roots / Q000648:ultrastructure; D012441:Saccharomyces cerevisiae / Q000648:ultrastructure
chemical_list: D008565:Membrane Proteins
references.citation: Proc Natl Acad Sci U S A. 1976 Nov;73(11):3891-5
references.pmid: 1069273
references.citation: J Cell Biol. 1963 Jun 1;17(3):609-28
references.pmid: 19866628
references.citation: J Ultrastruct Res. 1967 Aug;19(3):283-303
references.pmid: 4167849
references.citation: Proc Natl Acad Sci U S A. 1966 May;55(5):1048-56
references.pmid: 5334198
references.citation: J Cell Biol. 1969 Jul;42(1):296-307
references.pmid: 4182374
references.citation: Z Zellforsch Mikrosk Anat. 1968;91(4):586-603
references.pmid: 4882176
references.citation: Adv Protein Chem. 1959;14:1-63
references.pmid: 14404936
references.citation: J Biophys Biochem Cytol. 1957 Jan 25;3(1):45-60
references.pmid: 13416310
references.citation: Exp Cell Res. 1964 Nov;36:285-96
references.pmid: 14254211
references.citation: Exp Cell Res. 1967 Mar;45(3):703-7
references.pmid: 5336898
references.citation: Science. 1967 Nov 3;158(3801):655-7
references.pmid: 4860951