Biological water: Its vital role in macromolecular structure and function.

Water in tissues and cells is confined by intervening cellular components and is subject to structural effects that are not present in its bulk counterpart. The structuring effects lower the dielectric susceptibility of water molecules and induce a "red shift" of their relaxation frequency. This is also a source of polarization fields that contribute to the effective interactions between macromolecules. The behavior of water molecules at hydrophilic sites is different from that at hydrophobic sites, and this dissimilar behavior promotes the anisotropy of the hydration shell of proteins. The anisotropy of the hydration shell is essential for the enzyme function, but it is also important in detecting denaturation of the protein (i.e., proteins expose their hydrophobic parts to water during unfolding). The most significant differences between biological and ordinary water will be presented along with how this information can be used to decipher patterns in dynamical behavior of biological water and to detect possible structural changes of the cellular components.