Danielli

Our knowledge of biological membrane ultrastructure has increased considerably over the years as a result of rapid advances in instrumentation. Although there is still controversy over the most correct biological membrane model, the concept of membrane structure presented by Davson and Danielli of a lipid bilayer is perhaps the one best accepted [12,13]. The most current version of that basic model, illustrated in Fig. 7, is referred to as the fluid mosaic model of membrane structure. This model is consistent with what we have learned about the existence of specific ion channels and receptors within and along surface membranes. 

JF Danielli, H Davson. A contribution to the theory of permeability of thin films. J Cell Comp Physiol 5 495-508, 1935. 

H Davson, JF Danielli. The Permeability of Natural Membranes. 2nd ed. New York Cambridge University Press, 1952. 

Figure 7.2 Danielli-Davson membrane model. A layer of protein was thought to sandwich a lipid bilayer.

The first membrane model to be widely accepted was that proposed by Danielli and Davson in 1935 [528]. On the basis of the observation that proteins could be adsorbed to oil droplets obtained from mackerel eggs and other research, the two scientists at University College in London proposed the sandwich of lipids model (Fig. 7.2), where a bilayer is covered on both sides by a layer of protein. The model underwent revisions over the years, as more was learned from electron microscopic and X-ray diffraction studies. It was eventually replaced in the 1970s by the current model of the membrane, known as the fluid mosaic model, proposed by Singer and Nicolson [529,530]. In the new model (Fig. 7.3), the lipid bilayer was retained, but the proteins were proposed to be globular and to freely float within the lipid bilayer, some spanning the entire bilayer. 

M. M. Dubinin, Physical Adsorption of Gases and Vapors in Micropores, in Progress in Surface and Membrane Science, D. A. Cadenhead, J. F. Danielli, and M. D. Rosenberg, eds. [Academic Press, New York, 1975], pp. 1-70. 

Danielli, J. F., Moran, J. F., Triggle, D. J. ed. Fundamental concepts in drug receptor interactions. New York Academic Press (1970). 

Sweetoiing agents thaumatin/ca. 22,000 MW prrtein, in different forms fruits of Thaumatococcus danielli Benth., Marantaceae, Ang. from W Afnca... 

At present there is considerable interest in the way in which the con-stituents of membranes are associated to form the dynamic complex entity of the cell membrane. Speculations range from the Danielli-type structure, first advanced in 1935, to structures which now place greater emphasis on the so-called hydrophobic bonding of the lipid polymethylene chains and amino acids of the membrane protein (10). Various other speculations about the associations of the membrane components are built around these two main themes. In a field of research where there are such a considerable speculation and divergence of opinion, this usually indicates a shortage of experimental information rather than variations in perspicacity. This seems to be true of our present knowledge of membrane structure. 

It is possible that quite different molecular architectures may occur in membranes from different sources. Current research may result in a much more dramatic revision or complete rejection of the bilayer model for some membranes, especially in such systems as mitochondria (30) and chloroplasts (2). However, it is also possible that structural differences are only variations on the basic theme of the bilayer, from myelin at one extreme to mitochondria or chloroplasts on the other. One must not readily reject the fundamentals of the Danielli concept, especially in view of the present inadequate knowledge of the properties of phospholipids in water. Clearly the molecular architecture of membranes is speculative, but most aspects of the problem are amenable to direct experimental test by the new physical techniques. A consistent model for biological membranes will emerge quickly. 

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