TRANSPORT OF THYROGLOBULIN AND PEROXIDASE IN THYROID FOLLICLE CELL

The nature of the protein(s) in the exocytotic vesicles in the thyroid follicle cells was explored, and whether or not thyroglobulin and peroxidase are transported by the same vesicles through the apical region of the cells to the follicle lumen was ascertained. Rats were pretreated with thyroxine for 2 days in order to inhibit endocytosis. A fraction of exocytotic vesicles was isolated by centrifugation in continuous and discontinuous sucrose density gradients. The protein content of the vesicles was analysed by electrophoresis in continuous polyacrylamide gradient gels. The vesicles contained (uniodinated) thyroglobulin, 12-S protein and thyralbumin. Parallel histochemical studies in the EM revealed that the same exocytotic vesicles contained peroxidase. These observations have important bearings on the mechanisms for thyroglobulin iodination, since it has been demonstrated that iodination does not occur in the exocytotic vesicles but in connection with the opening of the vesicles at the apical cell surface.