The energetics, density, mobility, and other properties of water molecules that interact with other molecules in living cells differ dramatically from those of ordinary water. When proteins, which are synthesized as amino acid chains, fold up to compact, biochemically active structures, and when enzymes bind the molecules on which they act during metabolism, hydrating water is expelled from the interacting surfaces. Its changes in density, detected by volume changes, give insight into fundamental life processes.
Read the article at Protein Science