The properties of thyroglobulin. I. The effects of alkali.

Several studies have appeared in the past 25 years (l-5) concerning the physicochemical properties of thyroglobulin, the protein precursor of the thyroid hormone thyroxine. Most of this work has utilized hog thyroid gland as a source of material. The various investigations are in rather good agreement in obtaining a molecular weight for thyroglobulin close to -$ million. Moreover, this form of the protein appears to be stable within the pH range -5.0 to 11.3 when neutral salt is present (1). Lundgren and Williams (2) in 1939 and O’Donnell et al. (5) recently have reported the appearance of a derivative of hog thyroglobulin, which sedimented with a substantially reduced sedimentation coefficient, when the free electrolyte was removed by extensive dialysis. Similar results have been obtained in the present study with calf thyroglobulin at low ionic strengths. However, the interpretation of data obtained on charged macromolecules, when investigated with insufficient amounts of salt to suppress electrostatic interactions, is usually not free of ambiguities. With thyroglobulin extracted from calf thyroid tissue, a new component, which possessed quite similar sedimentation properties to that reported by Lundgren and Williams, was observed to form at higher ionic strengths when the pH was raised above the neutral range. More extensive data, which can be interpreted with greater confidence, have been collected on this form of thyroglobulin. Further conformational changes’ of calf thyroglobulin at still higher pH values are also reported.