Structural Role of Water in Lipoprotein Systems
In a previous communication  the author has demonstrated that a water monolayer adsorbed between protein and lipids could account for many properties of biological membranes, including the conduction of electrical energy. Studies on the conductivity of wet protein [2–6] have already led to the conclusion  that the absorbed water probably was responsible for this conductivity. On the other hand, E i g e n  and then K l o t z  have described a mechanism whereby protons (or electrons) could jump bucket-brigade fashion from one water molecule to another, thus travelling long distances. This mechanism was first advanced  to explain the fact that the conductivity of ice is much larger than that of water. However, a close fit of water molecules in an ordered lattice is a perquisite in this mechanism. Thus an ice-like lattice would have to be postulated for the adsorbed water monolayer. It would be also necessary to demonstrate that the parameters of this lattice fit those of proteins and lipids so that both could be linked to the water monolayer by hydrogen bonds. There have been proposed for this lattice, parameters  which have been calculated by assuming in the monolayer a symmetrical hexagonal distribution of water molecules linked by 2.77 Å hydrogen bonds. Each water molecule therefore would have one unlinked hydrogen directed either toward one or the other side of the monolayer and capable of hydrogen bonding with either protein or lipids. Because in this arrangement the H—O—H angle of liquid water, 104° 45′ [9–11], would have to be preserved , the distance between second neighbour water molecules would be 4.63 Å instead of 4.50 Å as in ice . This parameter precisely corresponds to the largest cross-sectional dimension of fatty acid chains  and also to parameters of proteins . It would thus be possible to arrange lipid chains side by side in orderly array. The possible arrangement of the protein is less obvious. The purpose of the present communication is to demonstrate with exact models that protein chains in the keratin configuration could be linked to a water monolayer of the above description through hydrogen bonding involving both the carbonyl groups of the chain backbone and the polar amino acid side chains. For this purpose, photographs and diagrams derived from Dreiding models and one actual model are presented.
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