The dielectric estimation of protein hydration

Microwave dielectric measurements on six aqueous protein solutions are analyzed in terms of water ‘irrotationally bound’ to the protein, i. e. unable to rotate in the high-frequency field. Estimates are made of the maximum amount of bound water, i. e. water carried through the solution with the protein, as a function of axial ratio, assuming a spheroid molecule. Taking hydration estimates in conjunction with other data, we conclude inter alia: (1) That the β-lactoglobulin and egg-albumin molecules approximate to prolate rather than to oblate spheroids. (2) That a large proportion of the charged groups in horse methaemoglobin ‘protrude’ from the surface of the molecule.