Globulin iodinated

The thyroid hormone thyroxine (tetraiodo-thyronine, T4) and its active form triiodothyronine (T3) are derived from the amino acid tyrosine. The iodine atoms at positions 3 and 5 of the two phenol rings are characteristic of them. Post-translational synthesis of thyroxine takes place in the thyroid gland from tyrosine residues of the protein thyro-globulin, from which it is proteolytically cleaved before being released, iodothyronines are the only organic molecules in the animal organism that contain iodine. They increase the basal metabolic rate, partly by regulating mitochondrial ATP synthesis, in addition, they promote embryonic development. 

Oral contraceptives have their most significant effect on endocrine parameters. Blood cortisol, thyroxine, protein-bound iodine, T3 uptake, and urinary free cortisol are elevated. Urinary 17,21-dihydroxy steroids, 17-ketosteroids, and estrogens are decreased. There is no effect on urinary catecholamines or VMA (Table 10) (LIO). The effect of thyroid functions tests is due to the administered hormone stimulating an increase in the production of thyroid-binding globulin which in turn binds 1-thyroxine. The lowering of free thyroxine stimulates the anterior pituitary to produce thyrotropin, which in turn stimulates the thyroid to produce more thyroxine. Since the additional thyroxine is bound to the extra protein, there is an equilibrium and the patient remains clinically euthyroid, but the protein-bound iodine and the thyroxine are elevated. 

Oral contraceptives can cause an increase in total thyroxine (163) and a fall in the percentage of free thyroxine (164). The uptake of radioactive iodine in the thyroid is usually normal total uptake of radioactive iodine may be reduced (164). The effect of progestogens on thyroxinebinding globulin may possibly counteract the estrogenic action. The net result will be a rise in protein-bound iodine and a fall in resin triiodothyronine uptake (165). It has been suggested that oral contraceptives may actually have some protective effect against thyroid disease. 

In all cases, the tubes were allowed to stand for 1 hour at room temperature, following which iodinated APS-314d (4000 cpm) was added in 0.05 ml of assay buffer to all tubes, as well as to 3 tubes labeled as total radioactivity . With the exception of the latter, the tubes were vortexed for a few seconds and then they received 0.05 ml of a mixture containing anti-beraprost serum (1 50,000 dilution) sheep anti-rabbit y-globulins (200 pl/ml) and rabbit y-globuhns (200 ig/ml) (the quantity of rabbit y globulins involved depends on the quality of the purihed sheep anti-rabbit y-globulins serum and must be checked with each preparation of this second antibody). 

Standard point Samples Human blank plasma Assay buffer Iodinated APS-314d Mixture containing rabbit anti-Beraprost serum, sheep anti-rabbit y-globulins and rabbit y-globulins... 

LE. High specific activity iodination of gamma-globulin with 64. iodine-131 monochloride. Cancer Res. 1960 20 1495-1500. 

Behaves like a globulin with a broad isoelectric zone. Biological activity is destroyed by heating and by proteolysis with pepsin, trypsin, and chymotrypsin. Also inactivated by oxidizing agents, such as potassium permanganate and elemental iodine. 

For antigens that are unusually labile, it may be better to iodinate the antibody rather than the antigen. The antibody that contains numerous tyrosine residues can be substituted with several iodine molecules without adverse effects on antibody activity. The antibody is radiolabeled with usually after specific purification with antigen, to reduce or eliminate labeling of nonspecific gamma globulins. 

Due to the ease of handling and efficiency, the Chloramine-T method is still the most widely used radioiodination procedure and represents an effective way to label a variety of proteins and peptides such as albumins, globulins, neuropeptides, and chemokines. Several other methods, such as the enzymatically catalyzed iodination with lactoperoxidase, have been developed. These methods allow the labeling with mild reaction conditions. In the case of extreme oxidation, sensitive proteins such as pituitary hormones and reactive pre-iodinated compounds such as the Bolton and Hunter reagent can be used to incorporate radioiodine. 

It is not well known at what stage of the thyroglobu-lin molecule s biosynthesis tyrosine is iodinated. Three proposals have been submitted (1) iodination of the amino acid before its incorporation into the polypeptide chain (but puromycin does not impair iodination, and no enzymes capable of activating iodotyrosine have been found) (2) iodination of the finished tetra-meric globulin and (3) iodination of the 12 S subunits with concomitant condensation of the unit to yield new protein. However, there seems to be no doubt that thyroglobulin continues to be iodinated even after its excretion into the colloid, indeed the ratio... 

Kleczkowski (167) has indicated that in iodinated serum globulin the diiodotyrosine yields no color with the Folin s phenol reagent and that the color obtained arises from the tryptophan. This is surprising in view of the fact that pure diiodotyrosine produces at least 50% of the color of tyrosine. It is possible that in this instance the tyrosine has been oxidized as well as iodinated. The phenol color value of tyrosine oxidized by iodine is reported (70) as 20% or less of the original tyrosine. 

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