Mono-iodotyrosines

MMI, TZD (6), PYSH (7), PMT (10), MNA (8) and MBA (9) on the other hand that strongly bind to or are oxidized to disnlfides [15] most probably interfere in the formation of mono-iodotyrosine (MIT), di-iodotyrosine (DIT) by the tyrosine residnes of thyroglobnline Tyr(TG), competing with active iodine. 

The result of iodination at tyrosine groups can alter the spectral characteristics of the protein in solution (Hughes and Straessle, 1950). The typical protein absorbency at 280 nm can shift to a maximum at about 305—315 nm due to the addition of iodine atoms to the phenolate ring of tyrosine. The degree of absorbance shift is dependent on how many iodine atoms are incorporated into the protein and whether they result in mainly mono-iodotyrosine or di-iodotyrosine formation. In addition, as the level of... 

Crystalline mono iodotyrosine was also isolated from pepsin treated with a small quantity of iodine (7). Some of its properties did not agree with those of synthetic mono iodotyrosine so that its exact nature has been questioned (297). The isolation from peptin has been repeated and a comparison made with a synthetic product. Such properties as solu-> bility, ultraviolet absorption spectra, pK s, and distribution coefficients were compared and cross-examined wherever possible. There can be no doubt that the crystalline product from pepsin is mono iodotyrosine (298). 

Butanol-extractable iodine (BEl) methods. These were regarded as an improvement on the FBI, although they are now little used because they are difficult to perform and imprecise. They consist of extracting the serum with n-butanol. This extracts thyroxine, T3, mono-iodotyrosine, di-iodotyrosine and inorganic iodide. The butanol extract is washed with alkali which removes mono and di-iodotyrosines and inorganic iodide. The butanol extract, which now contains mostly thyroxine and T3, can be... 

MIH " monoiodohistidine, 1 = iodides, DIH = diiodohistidine MIT mono-iodotyrosine, DITh = diiodothyionine, TRITh triiodothyronine, Tx = thyroxine. 

Thyroid hormone synthesis requires oxidation of dietary iodine, followed by iodination of tyrosine to mono- and diiodotyrosine coupling of iodotyrosines leads to formation of the active molecules, tetraiodo-tyrosine, (T or L-th3rroxine) and triiodotyrosine (Tj or L-thyronine). 

This peroxidase catalyzes two important reactions in the thyroid hormone synthesis (i) the iodination of tyrosines in thyroglobulin to yield protein-bound mono- and di-iodotyrosines... 

Theoretically, the condensation of mono- and diiodotyrosine could yield four different compounds 3,3 -diiodothyronine, 3,3, 5 -triiodothyronine, 3,5,3 -triio-dothyronine, and thyroxine (see Fig. 8-4). The exact mechanism of the formation of these various iodinated derivatives is not clear, but it has been suggested that they are formed by the condensation of two molecules of iodotyrosines with loss of a side chain. In this reaction, the iodinated tyrosine is converted by the loss of two atoms of hydrogen to the quinoid form, which acts as a free radical and condenses with other molecules of iodinated tyrosine to yield a diphenyl ring. During such a reaction, an oxygen bridge is formed, and one of the side chains of tyrosine is split to yield an a-amino acrylic acid. The a-amino acrylic acid is further metabolized to yield ammonia and pyruvic acid. 

According to Sohneideb [229], monoiodotyrosine hRf 25), di-iodotyrosine, diiodothyronine, triiodothyronine and thyroxine (hB/ 46) can be separated in that order of increasing hB/-values on silica gel 6 layers using 95% acetic acid-benzene-xylene (60 + 20 + 20). For the most part however, only mono- and diiodotyrosine have been chromatographed along with tyrosine [217]. These three compounds can be satisfactorily separated with butanol-acetic acid-water (40 + 10 + 50) or (100+ 10+ 10), butanol-methanol-20 % ammonium hydroxide (80... 

A method of thyroid hormone estimation which consists of extracting iodinated amino acids from serum using n-butanol. The extract is washed with alkali which removes inorganic iodine and mono- and di-iodotyrosines, leaving behind triiodothyronine and thyroxine. The butanol extract can then by evaporated to dryness and analysed for iodide content. 

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