Thiamine phosphorylation

Hyland S, Muller D, Hayton S, Stoeckhn E, BareUa L (2(X)6) Cortical gene expression in the vitamin E-deficient rat possible mechanisms for the electrophysiological abnormalities of visual and neural function. Ann Nutr Metab 50(5) 433-441 Heroux M, Raghavendra Rao VL, Lavoie J, Richardson JS, Butterworth RF (1996) Alterations of thiamine phosphorylation and of thiamine-dependent enzymes in Alzheimer s disease. Metab Brain Dis ll(l) 81-88... 

Molin, W.T., C.G. Wilkerson Jr, and R.C. Fites Thiamin phosphorylation by thiamin pyrophosphotransferase during seed germination Plant Physiol. 66 (1980) 313-315. 

ATP thiamin phosphotransferase kinase, thiamin (phosphorylating) thiamin kinase... 

Heroux, M., et al., 1996. Alterations of thiamine phosphorylation and of thiamine-dependent enzymes in Alzheimer s disease. Metab Brain Dis. 11, 81-88. 

Populational under-nutrition, decreased intake Low intake, under-nutrition, inhibition of intestinal and erythrocyte thiamine transport, inhibition of thiamine phosphorylation, reduction in liver stores, hypomagnesemia Used in heart failure, they increase loss of TDP and several other trace elements and minerals with urine... 

In the tissues of animals, most thiamine is found as its phosphorylated esteis (4—6) and is piedominandy bound to enzymes as the pyrophosphate (5), the active coen2yme form. As expected for a factor involved in carbohydrate metaboHsm, the highest concentrations ate generally found in organs with high activity, such as the heart, kidney, Hver, and brain. In humans this typically amounts to 1—8 p.g/g of wet tissue, with lesser amounts in the skeletal muscles (35). A typical healthy human body may contain about 30 mg of thiamine in all forms, about 40—50% of this being in the muscles owing to their bulk. Almost no excess is stored. Normal human blood contains about 90 ng/mL, mostly in the ted cells and leukocytes. A value below 40 ng/mL is considered indicative of a possible deficiency. Amounts and proportions in the tissues of other animal species vary widely (31,35). 

Scheme 2.—Phosphorylations and condensation in the biosynthesis of thiamine pyrophosphate.

From this observation of the inhibition by adenosine, and other observations, Newell and Tucker suspected the existence of a common synthetic pathway for adenosine and thiamine, and proved (with the help of a collection of mutants) that the bifurcation occurred after the 5-amino- l-(P-D-ribofura-nosyl)imidazole 5 -phosphate (46) step (Scheme 23). Finally, they found that 5-amino-l-(0-D-ribofuranosyl)imidazole (47), labeled with l4C in the imidazole ring, was incorporated into pyramine without significant loss of molar radioactivity by a mutant that is able to use this nucleoside (presumably after phosphorylation).53,54... 

In the form in which they are consumed, many vitamins are not biologically active. For several water-soluble vitamins such as thiamine, riboflavin, nicotinic acid, pyridoxine, activation includes phosphorylation or, as is the case with riboflavin and nicotinic acid, coupling to purine or pyridine nucleotides is required. In their major known actions, water-soluble vitamins participate as cofactors for specific enzymes, whereas at least two fat-soluble... 

Thiamine (vitamin Bi) is phosphorylated by ATP to thiamine pyrophosphate. This is a coenzyme for, among others, alpha-ketoglutarate dehydrogenase, transketolase and pyruvate dehydrogenase. Thiamine pyrophosphate is involved in fatty acid... 

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

Phosphorylation of dCDP to dCTP (step k, Fig. 25-14) completes the biosynthesis of the first of the pyrimidine precursors of DNA. The uridine nucleotides arise in two ways. Reduction of UDP yields dUDP (step), Fig. 25-14). However, the deoxycytidine nucleotides are more often hydrolytically deaminated (reactions / and / ) 274 Methylation of dUMP to form thymidylate, dTMP (step n, Fig. 25-14), is catalyzed by thymidylate synthase. The reaction involves transfer of a 1-carbon unit from methylene tetrahydrofolic acid with subsequent reduction using THF as the electron donor. A probable mechanism is shown in Fig. 15-21. See also Box 15-E. Some bacterial transfer RNAs contain 4-thiouridine (Fig. 5-33). The sulfur atom is introduced by a sulfurtransferase (the Thil gene product in E. coli). The same protein is essential for thiamin biosynthesis (Fig. 25-21)274a... 

Ascorbic acid, thiamine, riboflavin, and vitamin B12 requirements increase in hyperthyroidism (issue concentrations reduced Vitamin A massive doses of vitamin A inhibit secretion of TSH thyroid hormones required for carotene and retimene conversions Vitamins A, D, E. and K requirements increased in hyperthyroidism tissue concentrations reduced in Vitamin B, . niacin conversion to phosphorylated reactive forms impaired in hyperthyroidism... 

NADP+ differs from NAD+ only by phosphorylation of the C-2 OH group on the adenosyl moiety. The redox potentials differ only by about 5 mV. Why do you suppose it is necessary for the cell to employ two such similar redox cofactors Thiamine-pyrophosphate-dependent enzymes catalyze the reactions shown below. Write a chemical mechanism that shows the catalytic role of the coenzyme, (a) O O... 

Transketolase from common yeast (Saccharomyces cerevisiae) is commercially available, but it is possible to work with a partially purified enzyme, isolated with little expense from spinach leaves.54 Transketolase catalyzes the transfer of a hydroxyacetyl group, reversibly from a ketose phosphate, or irreversibly from hydroxypyruvate to an acceptor aldose, phosphorylated or not.55 It requires thiamine pyrophosphate as a coenzyme, but only in catalytic amounts. In all the cases listed in Table V, the new chiral center, C-3 of the ketose, has the l-glycero configuration. 

During the last two decades, the mechanisms of many enzymic processes have been established, and model systems have been developed that effectively mimic their action. In particular, the roles of thiamin, NAD, pyridoxal, flavins, Bl2, ferridoxin, and metals in many enzymic processes now are understood. Model systems have been developed to imitate the action of decarboxylases and esterases, to imitate the action of enzymes in binding their substrates, and to approach the stereospecificity of enzymes. Our laboratory recently has found phosphorylating agents that release monomeric methyl metaphosphate, which in turn carries out phosphorylation reactions, including some at carbonyl oxygen atoms, that suggest the actions of ATP. The ideas of biomimetic chemistry are illustrated briefly in terms of the processes mentioned above. 

Pyruvate produced by the glycolytic pathway may be transported into the mitochondria (via an antiport with OH"), where it is converted to acetyl-CoA by the action of the enzyme complex pyruvate dehydrogenase. The pertinent enzyme activities are pyruvate dehydrogenase (PD), lipoic acid acetyltransferase, and dihydrolipoic acid dehydrogenase. In addition, several cofactors are utilized thiamine pyrophosphate (TPP), lipoic acid, NAD+, Co A, and FAD. Only Co A and NAD+ are used in stoichiometric amounts, whereas the others are required in catalytic amounts. Arsenite and Hg2+ are inhibitors of this system. The overall reaction sequence may be represented by Figure 18.5. The NADH generated may enter the oxidative phosphorylation pathway to generate three ATP molecules per NADH molecule reduced. The reaction is practically irreversible its AGq = -9.4 kcal/mol. 

Figure 7-2. Reactions of the pyruvate dehydrogenase (PDU) multienzyme complex (PDC). Pyruvate is decarboxylated by the PDH subunit (I ,) in the presence of thiamine pyrophosphate (TPP). The resulting hydroxyethyl-TPP complex reacts with oxidized lipoamide (LipS3), the prosthetic group of dehydrolipoamide transacetylase (Ii2), to form acetyl lipoamide. In turn, this intermediate reacts with coenzyme A (CoASH) to yield acetyl-CoA and reduced lipoamide [Lip(SH)2]. The cycle of reaction is completed when reduced lipoamide is reoxidized by the flavoprotein, dehydrolipoamide dehydrogenase (E3). Finally, the reduced flavoprotein is oxidized by NAD+ and transfers reducing equivalents to the respiratory chain via reduced NADH. PDC is regulated in part by reversible phosphorylation, in which the phosphorylated enzyme is inactive. Increases in the in-tramitochondrial ratios of NADH/NAD+ and acetyl-CoA/CoASH also stimulate kinase-mediated phosphorylation of PDC. The drug dichloroacetate (DCA) inhibits the kinase responsible for phosphorylating PDC, thus locking the enzyme in its unphosphory-lated, catalytically active state. Reprinted with permission from Stacpoole et al. (2003).

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. 

Phosphorylation by ATP, catalyzed by thiamin diphosphate kinase, which acts only on protein-bound thiamin diphosphate and... 

Phosphorylation by ADP, catalyzed by adenylate kinase - this enzyme is especially important in the rapid synthesis and turnover of thiamin triphosphate in slow-twitch white muscle fibers. 

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