TMP kinase

Chenal-Francisque, V. Tourneux, L. Carniel, E. Christova, P. de la Sierra, L Barzu, O. Gilles, A.-M. The highly similar TMP kinase of Yersinia pestis and Escherichia coli differ markedly in their AZTMP phosphorylating activity. Eur. J. Biochem., 265, 112-119 (1999)... 

Tourneux, L. Bucurenci, N. Lascu, L sakamoto, H. Briand, G. Gilles, A.-M. Substitution of an alanine residue for glycine 146 in TMP kinase from Escherichia coli is responsible for bacterial hypersensitivity to bromodeoxyuridine. J. BacterioL, 180, 4291-4293 (1998)... 

Kandeel M, Ando T, Kitamura Y et al (2009) Mutational, inhibitory and microcalorimetric analyses of Plasmodium falciparum TMP kinase. Implications for drug discovery. Parasitology 136(1/11-25. Kandeel M, Kato A, Kitamura Y, Kitade Y... 

Thiamine is metabolized to TPP by thiamine pyrophosphokinase (EC 2.1.62) in animal cells including red and white blood cells. This enzyme is also present in plants, yeast, and a bacterium (Paracoccus denitrificans) (7). However, in some bacteria, for example in Escherichia coli, thiamine is metabolized to TPP by a two-step reaction catalyzed by thiamine kinase (EC 2.7.1.89) and TMP kinase (EC 2.7.4.10). Thiamine pyrophosphate is further metabolized to TI P in yeast, animal tissues, and human red blood cells. Evidence has been obtained which indicates that cytosolic adenylate kinase (EC 2.7.4.3) catalyzes TIP synthesis from TPP in vitro (8) and in vivo (3). The enzyme system involved in thiamine metabolism to TTP in human red blood cells was recently identified, purified, and reconstituted (9). 

F]-FLT is not or only marginally incorporated into DNA (<2%) and therefore not a direct measure of proliferation [122]. In vitro studies indicated that [ F]-FLT uptake is closely related to thymidine kinase 1 (TK1) activity and respective protein levels [117,118]. p F]-FLT is therefore considered to reflect TK1 activity and hence, S-phase fraction rather than DNA synthesis. Although being a poor substrate for type 1 equilibrative nucleoside transporters (ENT), cellular uptake of [ F]-FLT is further facilitated by redistribution of nucleoside transporters to the cellular membrane after inhibition of endogenous synthesis of thymidylate (TMP) de novo synthesis of TMP) [125]. However, the detailed uptake mechanism of [ F]-FLT is yet unknown and the influence of membrane transporters and various nucleoside metabolizing enzymes remains to be determined. 

Additional information <3> (<3> enzyme has 2 distinct domains related to TMP-PPase and HMP-P kinase activities [3]) [3]... 

Few pyrimidine bases are salvaged in human cells. However, the pyrimidine nucleosides uridine and cytidine can be salvaged by uri-dine-cytidine kinase, deoxycytidine can be salvaged by deoxycytidine kinase, and thymidine can be salvaged by the enzyme thymidine kinase. Each of these enzymes catalyzes the phosphorylation of a nucleoside(s) utilizing ATP, and forming UMP, CMP, dCMP, and TMP. 

Cells that have been preincubated with deoxyuridine, then exposed to [ H] thymidine, incorporate little or none of the labeled material into DNA. This is because of both dilution of the labeled material in the larger intracellular pool of newly synthesized TMP and also inhibition of thymidylate kinase by thymidine triphosphate. 

The answer is e. (Murray, pp 375-401. Scriver, pp 2663-2704. Sack, pp 121-138. Wilson, pp 287—320.) Orotic aciduria is the buildup of orotic acid due to a deficiency in one or both of the enzymes that convert it to UMP Either orotate phosphoribosyltransferase and orotidylate decarboxylase are both defective, or the decarboxylase alone is defective. UMP is the precursor of UTP, CTP, and TMP All of these end products normally act in some way to feedback-inhibit the initial reactions of pyrimidine synthesis. Specifically, the lack of CTP inhibition allows aspartate transcarbamoylase to remain highly active and ultimately results in a buildup of orotic acid and the resultant orotic aciduria. The lack of CTP, TMP, and UTP leads to a decreased erythrocyte formation and megaloblastic anemia. Uridine treatment is effective because uridine can easily be converted to UMP by omnipresent tissue kinases, thus allowing UTP, CTP, and TMP to be synthesized and feedback-inhibit further orotic acid production. 

Thymidine triphosphate (TTP) depletion. AZT and thymidine (T) compete with each other for phosphorylation by thymidine kinase into AZT-monophosphate (AZT-MP) and thymidine-monophosphate (TMP), respectively (Fig. 13) (Lynx and McKee 2006). AZT can therefore decrease the formation of TMP and TTP, whose relative deficiency can then slow mtDNA replication (Lynx and McKee 2006). Interestingly the administratimi of uridine in animals and perhaps also in humans can prevent AZT, ddC, and d4T toxicity (Walker and Venhoff 2005 Banasch et al. 2006). Uridine administration may provide an alternate route for TTP synthesis, thus preventing TTP depletimi and the impairment of mtDNA replication (Lynx and McKee 2006). Furthermore, the uridine-induced restoration of mtDNA levels and respiratory chain functirm could improve the activity of dihydroorotate dehydrogenase, a key mitochondrial enzyme involved in pyrimidine synthesis. Thus, a virtuous circle is initiated by uridine supplementation (Setzer et al. 2008). 

Fig. 14. Effect of 5-fluorouracil (5-FU) and 5-fluorodeoxyuridine (5-FdUMP) on the synthesis of RNA and DNA. 5-FU is incorporated into RNA whereas 5-FdUMP inhibits thymidilate synthetase competitively and blocks DNA synthesis. The conversion of thymidine (dTr) into thymidilate (dTMP) by means of thymidine kinase is only a subsidary routine to thymidilate which can become important, however, under certain conditions such as in developing pollen (page 185). U = uridine triphosphate, Tr = thymidine, TMP = thymidine monophosphate = thymidilate, TDP = thymidine diphosphate, TTP = thymidine triphosphate, 5-F = 5-fluoro, d = deoxy, 1 = thymidine kinase, 2 = thymidilate synthetase.

FIGURE 1. Biochemical pathways leading to the synthesis and utilization of thymidine monophosphate (TMP). TMP biosynthesis is effected both by the folate-dependent enzyme thymidylate synthetase (TS) and by thymidine kinase (TK). Using inhibitors of folate metabolism or lethal analogues of thymidine, the TS and TK pathways can be controlled to select for TK-competent or TK-deficient cells. For details, see text. 

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