Abstract
The relaxation time of thyroglobulin has been determined in water at. neutral pH, in concentrated urea and guanidine solutions, at alkaline pH, both before and after reduction with β‐mercaptoethanol. The structure of thyroglobulin in concentrated urea solutions is markedly affected by the pH, Time‐dependent changes occur in thyroglobulin in concentrated urea or guanidine solutions which arc observable by polarization of fluorescence but not by optical rotation or viscosity. The reduction of the disulfide crosslinks of thyroglobulin in urea at high pH or in guanidine produces linear polypeptide chains with few if any permanent contacts between segments.