DIELECTRIC MEASUREMENTS OF WATER SORBED ON OVALBUMIN AND LYSOZYME

A cell is described which makes it possible to measure the capacitance increments of water adsorbed on solid protein powders. The results demonstrate different forms of binding for successive increments of water sorbed by the protein. A capacitance isotherm shows two or more distinct segments. The first of these segments, with very small slope, is assigned to water bound by two hydrogen bonds to the protein. The second segment corresponds to the completion of a coverage of one molecule of water for each side-chain polar group. The capability of a sample to bind water tightly is found to be related to the extent to which the protein retains its native structure. For ovalbumin, the denatured material can adsorb more water and bind it more tightly than the native material, indicating that denaturation permits binding sites to approach one another in such a way that multiple bonds can be formed to the water molecules. Successive isotherms on the denatured material are superimposable, and cycles of adsorption and desorption of water on a given native sample change the shape of the isotherm toward that of the denatured material, indicating that the adsorption-desorption process itself has a denaturing effect. In contrast, changes in the capacitance isotherm of water on lysozyme indicate that the adsorption-desorption cycle renatures that material in terms of water-binding capability. © 1969.