THYREOGLOBULIN

From Big Medical Encyclopedia

THYREOGLOBULIN — the main protein of a thyroid gland, contains in covalently connected look practically all iodine which is in iron. At mammals, including and at the person, apprx. 80% of all proteins thyroid gland (see) falls to the share of T., however its true quantity depends on activity of gland. Iodine (see) is a part of T. in the form of the iodated amino acids — yodtironin (see) and yodti-rozin (see) and in structure of minor iodinated components; depends on a functional condition of a thyroid gland iodic exchange (see) in an organism. Absolute quantity and a ratio of the iodated amino acids in a molecule T. change depending on extent of its iodination. A ratio of iodtyrosines biologically more effectively in T., than in another, artificially iodated proteins.

T. represents the globular, high-structured glycoprotein (see. Glycoproteins ), the molecule of this protein contains more than 100 disulfide bridges (see. Sulphhydryl groups ). Pier. the weight (weight) 660 000, coefficient of sedimentation 19S (see. Sedimentation ). A carbohydrate part makes about 10% of all molecule T. also it is constructed approximately of 350 monosakharidny remains (a galactose, mannose, N-atsetilgeksozamina, sialine to - t and fukoza) organized in three types of the carbohydrate units covalently connected with the remains of asparagine, serine and threonine of a proteinaceous part of a molecule T.

Biosynthesis of a full molecule of 19S-thyreoglobulin consists of three consecutive processes. Polypeptide chain of T. it is synthesized on the ribosomes connected with membranes of a cytoplasmic reticulum (an endoplasmic reticulum) of a follicular cell of a thyroid gland. Glycosylation of a molecule T. occurs in the course of its migration towards a cavity of a follicle and comes to the end before the exocytosis, it is obvious in Golgi's complex. Iodination of T. it is carried out in an apical membrane of an epithelial follicular cell with the participation of enzyme of thyroperoxidase (tiroperoksidaza). Synthesized by T. collects in a cavity of a follicle.

Resorption of T., representing the first stage in the course of release of hormone, comes by transition of a colloid from a cavity of a follicle in cytoplasm of a follicular cell (endocytosis). Droplets of a colloid merge then with the lysosomes containing proteolytic enzymes therefore T. it is hydrolyzed and are released thyroid hormones (see. Tiroksin , Triiodothyronine ). However the normal thyroid gland leaves nek-paradise a part not split by T. (perhaps, through limf, ways though direct allocation of T is not excluded. in a capillary network). In giperplazirovanny gland secretion of T. it is raised. All stages of synthesis, migration and degradation of T. are under control of tireopnopny hormone (see).

Define T. by the methods specific for glycoproteins (see).


Bibliography: The guide to clinical endocrinology, under the editorship of V. G. Baranov, L., 1977; Thyroid hormones, under the editorship of. I. X. Turakulova, Tashkent, 1972; Tura to at l about in I. X., Babayev T. A. and With and and t about in T. Iodproteins of a thyroid gland, Tashkent, 1974.


I. X. Turakulov.

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