Purification and storage of thyroglobulin. Two important factors influencing the radioimmunoassay for thyroglobulin.

The effect upon the assay of the quality of the thyroglobulin (Tg) used as standard and tracer was evaluated by comparison of two preparations, one purified with protease inhibitors added (Tg-PI) and the other without (Tg-O). Tg-PI proved more stable than Tg-O. After freezing in phosphate-buffered saline almost all 125I-Tg-O was found to have dissociated into 12 S Tg, while only about half the 125I-Tg-PI had done so. Storage in glycerol, 500 g/l, at -20 degrees C or freezing in goat serum improved the quality of the 125I-Tg markedly, but Tg-PI still remained more stable than Tg-O. In addition, the two antisera tested gave different results in the radioimmunoassay with Tg-PI and Tg-O. With one antiserum a gradual loss of Tg immunoreactivity occurred parallel to the dissociation of Tg, while no such effect was noted with the other antiserum. This difference is believed to depend on varying proportions of conformational antibodies in the antisera, the binding sites for the conformational antibodies being distorted by the dissociation of the Tg molecule, while the binding sites for the sequential antibodies remain intact.