CORTICOSTEROID THE CONNECTING GLOBULIN (synonym transcortinum) — the transport protein of a blood plasma reversibly forming specific complexes with corticosteroids and progestins. Sandberg (A. Sandberg, 1957) with sotr is for the first time revealed in a blood plasma of the person almost at the same time by three groups of authors [Dodey (W. Daughaday, 1956)., Bush (I. Bush, 1957)].
To. it is found in 131 species of vertebrate animals; it is allocated in a high cleaning view from a blood plasma of the person, a rabbit, a rat, a Guinea pig.
To. is an alfa1-glycoprotein about a pier. weight it (is powerful) 40 000 — 60 000, consisting of one peptide chain covalently connected with a carbohydrate component. N-atsetilneyramino-vaya to - that, the squirrel who is a part of a carbohydrate part of a molecule, defines its ability to form specific complexes with corticosteroids (see) and progestins (see). The association constant of protein to these hormones usually makes apprx. 10 7 M - 1 at t ° 37 ° and 10 8 M - 1 at t ° 4 °. To. in fiziol, conditions it is strong, but reversibly connects apprx. 80% of the circulating corticosteroids (glucocorticoids) and progestins. The strongest complexes of squirrels forms with cortisol, corticosterone, progesterone, 17alfa-pregnenoldione, 11-dezoksikortizoly; the cortisone and Aldosteronum interact with it less intensively, adrogena communicate very poorly.
Estrogen, metabolites of corticosteroids, androgens and progestins, and also the majority of synthetic analogs of cortisol with To. practically do not interact.
To. it is formed in hepatocytes in the form of inactive protein of a pretranskortin which is activated, apparently, in a blood plasma; its period biol, half-decay (T 1/2 ) at the person makes 5 — 6 days. Biosynthesis To. it is regulated by a number of endocrine factors: are oestrogenic and pituitary factors of still unknown nature induce it, and androgens, some metabolites of corticosteroids and Prolactin — inhibit.
Kompleksirovaniye of corticosteroids and progestins with To. of plasma plays a buffer and reserve role in relation to hormones, regulating their receipt in cells from blood. Connected with To. hormones are reversibly switched off from spheres biol, actions, metabolism and a feedback mechanism. Creation of a labile hormonal reserve can stabilize active concentration of hormone in blood at fiziol, shifts of its secretion and metabolism. Special value buffer function K. gets, obviously, from pregnant women, causing optimum balance of hormones at mother and a fruit. Increase of contents is established To. (by 2 — 3 times) in plasma of pregnant women and some animal species with haemo chorial type of a placenta.
Interaction To. with corticosteroids it is quantitatively estimated in size of the connecting ability of protein in relation to the connected hormones, on a ratio and concentration of free and proteinaceous and connected forms of hormones. For determination of size of the connecting ability of protein (the maximum quantity of hormone, a cut can connect protein of plasma), methods are usually used gel filtering (see), solid-phase adsorptions (see), ultrafiltrations (see) and equilibrium dialysis (see). The last two methods are most reasonable for definition of a ratio and concentration of free and connected hormones in a blood plasma. The size of the connecting ability To. at the person normal it is equal to 20 — 30 mkg of % of the connected steroid; at pregnant women it can reach 40 — 60 mkg of %.
The connecting ability of protein can decrease at proteinaceous dystrophy, shock, a thyrotoxicosis, gipotalamo-pituitary insufficiency, some forms of a hypercorticoidism and to raise at collagenoses.
Bibliography: Biocomplexes and their value, under the editorship of S. I. Afonsky, etc., page 95, M., 1965; Modern questions of endocrinology, under the editorship of N. A. Yudayev, century 5, M., 1975; Human physiology and animals, t. 11 — Physiology of endocrine system, page 49 * M., 1973, bibliogr.; Westphal U. Steroid-Protein Interactions, B., 1971, Bibliogr.
V. B. Rosen.