Thiamine monophosphate

Fig. 32 shows a stepwise separation of broad zones of thiamine mono- and diphosphate on a CS-KU-2 cellosorbent. The dynamic criteria (A and A.) predict the zones limited by sharp boundaries with a complete yield of the components at pH 4.9 for thiamine diphosphate and at pH 6.5 for thiamine monophosphate. It is noteworthy that the criterion A predetermines the slow motion ot the thiamine... 

Fig. 32. Stepwise preparative desorption chromatography of phosphoric esters of thiamine on CS-KU-2 cellosorbent /) highly phosphoric thiamine esters, 2) thiamine diphosphate, 3) thiamine monophosphate, 4) thiamine, 5) impurities...

In brain, as in most mammalian cells, thiamine occurs predominantly in the form of TDP, the remainder being made up of thiamine monophosphate (10%), thiamine triphosphate (5-10%) and trace amounts of free thiamine. Thiamine is transported into brain and phosphory-lated by the action of thiamine pyrophosphokinase, and inhibition of this enzyme by thiamine antagonists such as pyrithiamine results in decrease synthesis of TDP. Treatment of experimental animals with pyrithiamine results in a generalized reduction of TDP concentrations and an early selective loss in activity of a-KGDH in regions... 

ATP thiamin-phosphate phosphotransferase kinase, thiamin monophosphate (phosphorylating) thiamin monophosphatase... 

Nishino, H. Biogenesis of cocarboxylase in Escherichia coli. Partial purification and some properties of thiamine monophosphate kinase. J. Biochem., 72, 1093-1100 (1972)... 

Webb, E. Downs, D. Characterization of thiL, encoding thiamin-monophosphate kinase, in Salmonella typhimurium. J. Biol. Chem., 272, 15702-15707 (1997)... 

Thiamin is synthesized in bacteria, fungi, and plants from 1-deoxyxylulose 5-phosphate (Eq. 25-21), which is also an intermediate in the nonmevalonate pathway of polyprenyl synthesis. However, thiamin diphosphate is a coenzyme for synthesis of this intermediate (p. 736), suggesting that an alternative pathway must also exist. Each of the two rings of thiamin is formed separately as the esters 4-amino-5-hydroxy-methylpyrimidine diphosphate and 4-methyl-5-((i-hydroxyethyl) thiazole monophosphate. These precursors are joined with displacement of pyrophosphate to form thiamin monophosphate.92b In eukaryotes this is hydrolyzed to thiamin, then converted to thiamin diphosphate by transfer of a diphospho group from ATP.92b c In bacteria thiamin monophosphate is converted to the diphosphate by ATP and thiamin monophosphate kinase.92b... 

As shown in Figure 6.1, thiamin consists of pyrimidine and thiazole rings, linked by a methylene bridge the alcohol group of the side chain can be esterified with one, two, or three phosphates, yielding thiamin monophosphate, thiamin diphosphate (also known as thiamin pyrophosphate, the metabolically active coenzyme), and thiamin triphosphate. The vitamin was originally named aneurine, the antineuritic vitamin, because of its function in preventing or... 

Figure 6.1. Thiamin and thiamin anaiogs, products of thiaminoiysis, and experi-mentai antimetahoiites. Reiative moiecuiar masses (Mr) thiamin, 266.4 (chioride-hydrochioride, 337.3) thiamin monophosphate, 345.3 thiamin diphosphate, 425.3 thiamin triphosphate, 505.3 thiochrome, 262.3 thiamin thioi, 282.4 (oxidizes to thiamin disuifide, 562.7) oxythiamin, 301.8 and pyrithiamin, 420.2.

Some thiamin is phosphorylated to thiamin monophosphate in the intestinal mucosa, although this is not essential for uptake, and isolated membrane vesicles wUl accumulate free thiamin against a concentration gradient. Thiamin does not accumulate in the mucosal cells there is sodium-dependent active transport across the basolateral membrane, so that the mucosal concentration of thiamin is lower than that in the serosal fluid (Hindi et al., 1984 Hindi and Laforenza, 2000 Dudeja et al., 2001). 

Both free thiamin and thiamin monophosphate circulate in plasma about 60% of the total is the monophosphate. Under normal conditions, most is bound to albumin when the albumin binding capacity is saturated, the excess is rapidly filtered at the glomerulus and excreted in the urine. Although a significant amount of newly absorbed thiamin is phosphorylated in the Uver, aU tissues can take up both thiamin and thiamin monophosphate, and are able to phosphorylate them to thiamin diphosphate and thiamin triphosphate. In most tissues, it is free thiamin that is the immediate precursor of thiamin diphosphate, which is formed by a pyrophosphokinase both the p-and y-phosphates of ATP are incorporated. Thiamin monophosphate arises mainly as a result of sequential hydrolysis of thiamin triphosphate and thiamin diphosphate. 

Both thiamin monophosphate and free thiamin are found in cerebrospinal fluid. Uptake of thiamin monophosphate into cells in the central nervous system involves extracellular hydrolysis to free thiamin, probably catalyzed... 

A small amount of thiamin is excreted in the urine unchanged, accounting for about 3% of a test dose, together with small amounts of thiamin monophosphate and thiamin diphosphate. As discussed in Section 6.5.1, this can be used to assess thiamin nutritional status. One of the major excretory products is thiochrome cyclization to thiochrome is the basis of the normal method of determining thiamin so, most reports of thiamin excretion are actually of thiamin plus thiochrome. In addition, small amounts of thiamin disulfide, formed by the oxidation of thiamin thiol, are also excreted. 

The final step in the synthesis of thiamin involves condensation between the hydroxymethylpyrimidine diphosphate andhydroxyethylthiazole monophosphate to yield thiamin monophosphate, which can then be dephosphorylated to free thiamin or phosphorylated further to the diphosphate and triphosphate (Hohmann and Meacock, 1998 Begley et al., 1999). 

Erythrocytes and leukocytes contain mainly thiamin diphosphate, whereas plasma contains free thiamin and thiamin monophosphate. The concentration of thiamin diphosphate in erythrocytes is normally between 110 and 330 nmol per L of packed cells. The total thiamin concentration in erythrocytes is about 4- to 5-fold higher than in plasma and that in leukocytes is 10-fold higher again. 

Patrini C, Reggiani C, LaforenzaU, and Hindi G (1988) Blood-brain transport of thiamine monophosphate in the rat a kinetic study invivo. Journal of Neurochemistry 50,90-3. 

Reggiani C, Patrini C, and Hindi G (1984) Nervous tissue thiamine metabolism in vivo. 1. Transport of thiamine and thiamine monophosphate from plasma to different brain regions of the rat. Brain Research 293,319-27. 

Thiamine uptaken into the cell is phosphorylated to TDP by the enzyme thiamine pyrophosphokinase. TDP is then further phosphorylated to thiamine triphosphate (TTP) or is dephosphorylated to thiamine monophosphate (TMP). 

Fig. 2 Intercellular trafficking and thiamine and thiamine esters in brain. TMP thiamine monophosphate, TDP thiamine diphosphate, TTP thiamine triphosphate, TPKinase thiamine pyrophosphokinase...

Vitamin Bj Vitamin Bj was discovered in 1926 by Jansen and Do-NATH, who synthesized it in its crystalline form from rice bran. It was initially called aneurine due to its antipolyneuropathic effect. Because it contains sulphur, Windaus correctly renamed it thiamine in 1932, a term by which it is still known today. The stixicture of this vitamin was described by Williams and Grewe in 1936. It is made up of pyrimidine and thiazole. Thiamine occurs in nature as free thiamine and in the form of thiamine monophosphate, diphosphate and triphosphate. A maximum amount of 8 — 15 mg is absorbed daily in the proximal portion of the small intestine. In the case of oversupply, thiamine is neither stored nor intestinally absorbed. A regular intake, with a daily requirement of about 1 mg, is necessary. The major coenzyme is thiamine pyrophosphate (TPP). Thiamine deficiency may be caused by malnutrition, impaired absorption, alcoholism, antithiamines or a lack of magnesium. Magnesium is an important cofactor for the coenzyme thiamine pyrophosphate. 

The cofactor form of thiamin is thiamiri pyrophosphate (TPP). TPPis released from dietary proteins during hydrolysis in the gastrointestinal tract and then hydroly 2ed to thiamin- The thiamin is absorbed and transported into various tissues, where it Is converted back to TPP by the action of thiaminokinase (Figure 9.70). A small proportion of the body s thiamin occurs as thiamin monophosphate (TMP) and thiamin trisphosphate (TTP). 

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