Chemistry and Biology of Proteins - F. Haurowitz 1953

Protein-Water Interaction
Immobilized Water

Although The amount of hydrate Water is only 20 to 50 g per 100 g of protein, the total amount of water retained by living tissue is significantly greater. In Muscles and parenchymal Organs, 20–30% protein corresponds to an average of 70–80% water, meaning that 100 g of protein accounts for 200–300 g of water. In gelatin gels and jellyfish Tissues, the water-to-protein ratio is much higher. It was once believed that these large quantities of water were bound to Proteins, as it was difficult to explain why free water did not drain out when muscles or other tissues were subjected to drainage. However, studies of organs and gelatin gels using the Methods described in the preceding sections have proven that the bulk of this water is free. It freezes at the same Temperature as ordinary water, exhibits the same solvent power, and there is no evidence to suggest it is bound to protein molecules. Consequently, it must be regarded as free water, mechanically trapped within the network of protein membranes and cellular protein fibers [32, 33].

The existence of solid gelatin gels containing only 2–3% protein indicates that 1 g of gelatin is capable of holding more than 30 g of water. Most of the water contained in tissues appears to be immobilized.