Characterization of thyroid follicular cell apical plasma membrane peroxidase using monoclonal antibody

Thyroid peroxidase (TPO) located in the apical plasma membrane of follicular cells was investigated by means of a membrane-immunofluorescent technique. The epitope of TPO recognized by a murine monoclonal antibody (mAb 30.1.2) was identified on the apical membrane surface. Trypsinization removed TPO immunoreactivity and enzymatic activity after 60 min of incubation at 37 degrees C. The epitope reappeared on the apical membrane surface after short term culture for 120 min without the addition of TSH. With TSH the time required for reappearance was only 30 min. TPO activity was regenerated under both conditions. Since dibutyryl cyclic AMP could not accelerate the reappearance of the epitope, it was thought that TPO reappearance is mediated by other than the adenylate cyclase-cyclic AMP system.