Volume 1

Contemporary classics in the life sciences / edited by James T. Barrett.

Date:
©1986-
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Contemporary classics in the life sciences / edited by James T. Barrett. Source: Wellcome Collection.

    34/400 (page 12)
    This week's citat JANUARY B 4 E J982 Robertsoa I D. The ultrastructure of cell membranes and their derivatives. Biochem. Soc. Symp. 16 :3-43, 1959. [Department of Anatomy, University College, London, England] Electron microscopic (EM) observations on many biological membranes as seen in thin section* were reviewed and interpreted in molecular terms based on an analysis of nerve myelin. A general model of membrane molecular architecture was presented em phasizing the ubiquity of the lipid bilayer and chemical asymmetry. [The SC/® in dicate that this paper has been cited over 455 times since 1961.] J. David Robertson Department of Anatomy Duke University Medical Center Durham, NC 27710 October 1, 1981 The paper reviewed a number of obser vations that I had made during the mid-1950s regarding the molecular architec ture of biological membranes. That decade began with many doubts about the exact role of the lipid bilayer in the molecular architecture of biological membranes, but it ended with a note of certainty expressed in this paper. Earlier work had suggested a crucial role for lipid bilayers in membrane structure. There was, however, doubt about how many were present, the manner in which proteins were associated with the lipids, and indeed whether or not any par ticular model could be applied generally. There were also doubts about whether or not there might be mosaic patches of pure protein contiguous with lipid regions. The EM studies reviewed dispelled the doubts about membrane thickness and led to the certainty that biological membranes con tained one, and only one, lipid bilayer and further that a useful general model of mem brane molecular architecture could be pro posed. About 1956 I applied two new develop ments in EM technique, permanganate fixa tion and epoxy embedding, and observed a triple-layered pattern in all cell membranes and membrane organelles studied. The membrane measured ~ 7.5 nm in thickness and appeared as a pair of dense strata each ~ 2 nm thick bordering a light central zone. The work provided the first direct evidence that nerve myelin consisted only of Schwann cell membranes to the resolution of the sections (~ 2 nm). Partly on the basis of these observations I stated that the basic pattern resulted from the presence of one lipid bilayer as the fundamental core structure. A general model was proposed consisting of a lipid bilayer with protein at or in its polar surfaces in the dense strata. The idea of asymmetry due to polysac charides in the outer surface was also ad vanced. This paradigm, called the unit mem brane model, was the first one to make ex plicit the principle that biological mem branes in general have one lipid bilayer as their basic structure. It resembled the earlier Danielli-Davson one but differed signifi cantly in that only one bilayer was stipulated along with chemical asymmetry At the time, these ideas met with con siderable resistance partly because perman ganate was a poor general fixative, but it is good and selective for membranes and revealed them in the manner that is now regarded as standard. Somehow the idea arose that I claimed all cell membranes were molecularly identical, a complete misinterpretation. Perhaps in my enthusias tic pursuit of getting across the idea that there was a common molecular architecture in membranes which could be defined, I gave the impression I was saying that all membranes were molecularly identical Perhaps the problem here was that I was thinking in terms of molecules while others were not. The hydrophobic core of the bilayer is now known to be sometimes traversed by hydrophobic polypeptide chains The model has been modified to take this into account but the main point was the establishment of the ubiquity of the bilayer, which I believe is now generally accepted I have recently published work in this field. 12 1. Bofe*roo* I D. The anatomy of biological interfaces. (Andreoli T E, Hofíman J F & Panestil D D. eds.) Physiology of mimbran* disorders New York: Plenum, 1978. p. 1-26. 2. - . The nature and limitations of electron microscopic methods in biology. (Andreoli T E, Hoffman J F A Panestil D D. eds.) Physiology of membrane disorders. New York: Plenum. 1973. p. 61-93.