Studies of Thyroglobulin of Hypophysectomized Rats.II. Nature of Thyroidal Iodoprotein After Hypophysectomy of Rats Previously Depleted of Colloid by Propylthiouracil1

Abstract

We have studied the protein which is iodinated following hypophysectomy in rats previously depleted of colloid by administration of propylthiouracil (PTU). Thyroids of rats fed an iodine-sufficient diet with PTU for 18 or 31 days contained a thyroglobulin-like protein with approximately 0.004 μg iodine/100 μg protein and a sedimentation value of 18S. Glands from rats fed PTU for the same period of time, then hypophysectomized and fed the diet without PTU, accumulated colloid and contained more extractable thyroglobulin than did the PTUonset controls; this iodoprotein from the hypophysectomized rats contained 0.27 μg iodine/100 μg protein, sedimented at 18S, and was almost completely disaggregated into half-molecules by dialysis at pH 10.8. Thyroids of PTU-withdrawn intact rats accumulated 19S thyroglobulin which contained 0.44 μg iodine/100 μg protein and was only partially disaggregated at pH 10.8. The per cent of iodine as thyroxine and the MIT to DIT ratio in each of the thyroglobulin preparations vari...