The structure of human thyroglobulin: Sedimentation equilibrium in 6 M guanidine hydrochloride

Abstract Reduced and alkylated human thyroglobulin has been studied by high speed sedimentation equilibrium in 6 M guanidine-HCl at various pH values and at several rotor speeds. Our results indicate that thyroglobulin is heterodispersed under these conditions. This heterogeneity appears to be due to a combination of the presence of polypeptide moieties of different size derived from the thyroglobulin structure and possible incomplete dissociation. Due to this molecular weight heterogeneity we observe a significant rotor speed dependence of the apparent molecular weight. It is clear, however, that the human thyroglobulin structure contains polypeptide chains of molecular weight significantly below 100 000 and as low as 50 000.