Living cells, as a rule, contain 15 to 25 per cent proteins and 75 to 85 per cent water. We now know that it is the sequences of amino acid residues in the proteins that underlie biological specificity and that the difference in the nature of one amino acid residue (in a protein containing hundreds) may produce profound differences in the behavior of the entire tissue of which this protein is a part.' Yet, important as the proteins are in the living phenomena, there can be no life unless there is also water. Thus, whether in the form of contractile proteins or functioning enzyme, living protoplasm always contains water; the unique behavior it manifests, reflects not the behavior of the proteins per se but that of the protein water sys-tems. The question arises: In what way does water serve this critical role?

Does it function merely as a solvent of a suitable dielectric property?

In recent years, considerable evidence has been collected, showing that this is not so. Water molecules in the close vicinity of proteins and other biologically important macromolecules appear to exist in a physical state different from that of normal water. Forslind, for example, suggested that in protein solutions, water molecules close to macromolecules may exist in a state between that of liquid and solid. Jacobsen" supported this basic concept with x-ray, dielectric, and nuclear magnetic resonance studies on macromolecular solutions. Szent-Györgyi' postulated an ice-like structure of water surrounding proteins; Klotz et al.? supported and further developed this "iceberg" concept. From x-ray diffraction studies, Beeman et al." concluded that serum albumin is surrounded by a layer of water which does not dissolve sucrose as normal water does. Similarly, Hearst and Vinograd" by density measurements reached the conclusion that water closely associated with DNA excludes alkali metal ion (see also, Ritland et al.)* The nuclear magnetic resonance studies of Berendsen" have shown that in native collagen and partially dried collagen, water molecules are restricted in their rotation and that they form chains in the collagen fiber direction, being oriented by the peptide amide bonds.

This text was written and published 1965 by Gilbert Ning Ling. Today Gerald H. Pollack and his research on water exclusion zones (EZ-Water) and the fourth phase of water are continuing to shed light about the intracellular, extracellular and EZ water surrounding our proteins.

*These studies were aided by Contract Nonr 1-2060-66, (NR 105-327) between the Office of Naval Research, Department of the Navy, and the Pennsylvania Hospital. The investigator was also supported by a Public Health Service Research Development Award (GM K3-19,032) from the National Institute of Health.

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