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TUNESUKE KUSAKABE, A Goitrous Subject with Structural Abnormality of Thyroglobulin, The Journal of Clinical Endocrinology & Metabolism, Volume 35, Issue 6, 1 December 1972, Pages 785–794, https://doi.org/10.1210/jcem-35-6-785
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ABSTRACT
This report consists of a study of a woman with goiter whose primary defect seems to be in an abnormal stereostructure of thyroglobulin. She showed a positive thiocyanate discharge of 131I by the thyroid. Activities of thyroid peroxidase, catalase, transaminase, keto-enol tautomerase, and protease were comparatively normal. 125I-labeled monoiodotyrosine injected into the patient was rapidly deiodinated. Since the iodine content of the goiter thyroglobulin was at a high normal level (0.78%), it is unlikely that an iodide organification defect is a primary abnormality in this case. The behavior of the thyroid protein obtained from the patient was indistinguishable from that of normal thyroglobulin in solubility, electrophoretic mobility, sedimentation velocity, and antigenicity. Spectrotitration of tyrosyl and iodoamino acid residues in native and in vitro iodinated goiter thyroglobulin was performed in water and in 8m urea, and the reactivity of these residues was assessed with N-acetyl imidazole. Although the sum of the aromatic groups in tyrosyl and iodoamino acid residues in goiter thyroglobulin determined in 8m urea was equal to that in normal thyroglobulin, about two-thirds of tyrosyl and monoiodotyrosyl residues, and the majority of diiodotyrosyl and thyroxyl residues, appeared to be strongly buried inside the protein molecule, since these were not demonstrated in water. The number of tyrosyl residues that were easily accessible to iodide was about one-third of that in normal thyroglobulin. The percent of radioiodine bound to the goiter thyroglobulin by in vitro peroxidation also was one-third of that bound to the normal thyroglobulin. In vivo labeled goiter thyroglobulin proved to be resistant to the liberation of 125I from the results of its hydrolysis with protease. Thus, it may be presumed that the thyroglobulin of the present patient has abnormally compact internal structure of the molecule. Such a thyroglobulin may result in a reduced rate of thyroid hormone synthesis and release, and this may be a cause of goiter.
