Purification and some properties of microsome-bound thyroglobulins.

The sonicate of microsomal fraction of hog thyroid was found to contain two species of proteins which reacted with anti-thyroglobulin antiserum and corresponded to 2 to 3% of total protein of the fraction. The two species were purified by ammonium sulfate precipitation, repeated sucrose density gradient centrifugations and separated from each other by polyacrylamide gel electrophoresis into S-mb thyroglobulin (the slower-migrating microsomal-bound fraction), F-mb thyroglobulin (the faster-migrating microsomal-bound fraction), and thyroglobulin itself. Amino acid compositions of the proteins were essentially the same as that of thyroglobulin. Mannose contents also were close to that of thyroglobulin while galactose and fucose contents decreased in the order: thyroglobulin, F-mb thyroglobulin and S-mb thyroglobulin. S-mb thyroglobulin had no sialic acid and no iodine at all. F-mb thyroglobulin was sialylated to an extent of less than 80% of, and iodinated to an extent of less than 50% of that of thyroglobulin, respectively. Antigenic activities of F-mb thyroglobulin and of S-mb thyroglobulin were qualitatively the same as, but quantitatively less than, that of thyroglobulin. Sedimentation coefficients of S-mb thyroglobulin and F-mb thyroglobulin were approximately 1 S lower than that of thyroglobulin. All the properties of the thyroglobulin-related proteins suggested that S-mb thyroglobulin and F-mb thyroglobulin were the products by the sequential modification of thyroglobulin polypeptide in the pathway of thyroid hormone production.