SynopsisThe electrical conductivity of bovine Achilles tendon with various amounts of adsorbed water was measured as a function of temperature. The conduction appeared t.0 be fully determined by the water of hydration. The current is probably primarily carried by protons a t water contents up to 45% and by small ions a t water contents beyond 65%. In both ranges of water content, a linear relation between activation energy and water content was found. As to the lower range, this is explained by the action of Coulombic forces during the separation of protonshydroxyl ion pairs. In two regions of water content a linear relation between the logarithm of the pre-exponential factor and the activation energy was found. There are, however, no indications that a compensation effect is responsible for this observation. It is concluded that at certain water contents the dissociation constant of the adsorbed water is several orders of magnitude higher than in liquid water.

SynopsisDeterminations of the amount of bound water in hydrated proteins yield strongly diverging values. The cause of this is the continuity of the transition from bound to free water, and the different sensitivities to water structure of the measuring techniques. Only the methods that aim at the determination of the amount of water, whose phase remains unchanged during freezing, yield similar values. The value for collagen as deduced from conductivity data is about 50% water of the dry weight. It is believed that this water interacts with adsorptive groups on the macromolecules, whereas the freezable water occurs in capillaries.