5.10- Methylenetetrahydrofolate

Fig. 8. Thymidylate synthase inhibitors designed to fit into the A/, AJ -methylenetetrahydrofolate binding site. The best inhibitors from each class are the classical antifolate TS inhibitor (31), the naphthostyril-based lead compound (32), and the tetrahydroquinoline-based lead compound (33), iC values (in nAI)...

MA J, STAMPFER M J, GIOVANNUCCI E, ARTIGAS C, HUNTER D J, FUCHS C, WILLETT W C, SELHUB J, HENNEKENS c H and ROZEN R (1997) Methylenetetrahydrofolate reductase polymorphism, dietary interactions, and risk of colorectal cancer . Cancer Res, 57, 1098-102. 

Fig. 14.3 5 -FU catabolism, anabolism and mechanism of action. 5-FUH2, 5-fluoro-5,6-dihydrouracil 5-FdUMP, 5-fluorodeoxyuridine monophosphate TP, thymidine phosphorylase TK, thymidine kinase TS, thymidylate synthase CH2THF, 5,10-methylenetetrahydrofolate.

TK), 5-FU is activated to 5-fluorodeoxyuridine monophosphate (5-FdUMP). Potent inhibition of thymidylate synthase (TS) by 5-FdUMP is considered critical for 5-FU cytotoxicity. TS catalyzes the rate-limiting step of DNA synthesis, such as the conversion of dUMP into dTMP. Optimal TS function requires the formation of a covalent ternary complex consisting of TS, the folate cofactor 5,10-methylenetetra-hydrofolate (CH2THF), and 5-FdUMP. Inadequate cellular levels of 5,10-methyle-netetrahydrofolate reduce the stability of the ternary complex and consequently the inhibition of TS by 5-FdUMP. For this reason, 5-FU is administered in association with folinic acid, a precursor of 5,10-methylenetetrahydrofolate [40]. 

Fig. 14.10 Folate metabolism and role of MTHFR. Genetically reduced MTHFR activity affects the distribution between folate species required for protein and DNA synthesis. Higher availabil ity of 5,10-methylenetetrahydrofolate (CH2THF) potentiates the TS inhibition by 5-FdUMP, the active metabolite of 5-FU. Hey, homocysteine Met, methionine CH3HF, 5-methyltetrahydrofolate TS, thymidylate synthase 5-FdUMP, fluorodeoxyuridine monophosphate.

Bagley PJ, Selhub J. A common mutation in the methylenetetrahydrofolate reductase gene is associated with an accumulation of formylated tetrahydrofolates in red blood cells. Proc Natl Acad Sci USA 1998 95 13217-13220. 

Brattstrom L, Zhang Y, Hurtig M et al. A common methylenetetrahydrofolate reductase gene mutation and longevity. Atherosclerosis 1998 141 315-319. 

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the NAD(P)H-dependent reduction of 5,10-methylenetetrahydrofolate (CH2-THF) to 5-methyltetrahydrofolate (CH3-THF). CH3-THF then serves as a methyl donor for the synthesis of methionine. The MTHFR proteins and genes from mammalian liver and E. coli have been characterized,12"15 and MTHFR genes have been identified in S. cerevisiae16 and other organisms. The MTHFR of E. coli (MetF) is a homotetramer of 33-kDa subunits that prefers NADH as reductant,12 whereas mammalian MTHFRs are homodimers of 77-kDa subunits that prefer NADPH and are allosterically inhibited by AdoMet.13,14 Mammalian MTHFRs have a two-domain structure the amino-terminal domain shows 30% sequence identity to E. coli MetF, and is catalytic the carboxyterminal domain has been implicated in AdoMet-mediated inhibition of enzyme activity.13,14... 

Fig. 2.4 The S-methylmethionine cycle and its interaction with the activated methyl cycle. The SMM cycle operates within the activated methyl cycle, and in effect short-circuits it. The reactions mediated by MMT and HMT are shown in bold. THF, tetrahydrofolate CH2-THF, 5,10-methylenetetrahydrofolate,...

SHEPPARD, C., TRIMMER, E., MATTHEWS, R.G., Purification and properties of NADH-dependent 5, 10-methylenetetrahydrofolate reductase (MetF) from Escherichia coli,J. Bacteriol., 1999,181, 718-725. 

MATTHEWS, R.G., SHEPPARD, C GOULDING, C., Methylenetetrahydrofolate reductase and methionine synthase biochemistry and molecular biology, Eur. J. Pediatr., 1998,157, S54-S59. 

GOYETTE, P., PAI, A., MILOS, R., FROSST, P., TRAN, P., CHEN, Z., CHAN, M.,.ROZEN, R., Gene structure of human and mouse methylenetetrahydrofolate reductase (MTHFR), Mamm. Genome, 1998,9,652-656. 

RAYMOND, R.K., KASTANOS, E.K., APPLING, D.R., Saccharomyces cerevisiae expresses two genes encoding isozymes of methylenetetrahydrofolate reductase, Arch. Biochem. Biophys., 1999,372, 300-308. 

VANONI, M.A., MATTHEWS, R.G., Kinetic isotope effects on the oxidation of reduced nicotinamide adenine dinucleotide phosphate by the flavoprotein methylenetetrahydrofolate reductase, Biochemistry, 1984, 23, 5272-5279. 

In living systems, folinic acid can be synthesized ultimately from folic acid by reduction to tetrahydrofolic acid followed by addition of a 1-carbon fragment to the molecule (N5.N1°-methylenetetrahydrofolate, V). After a 2-step oxidation, the formyl group resides either at the N5 or N10 position or as an equilibrium mixture. The essential reactions are summarized below 32... 

Recently, the enzymatic formation of folinic acid has been utilized to synthesize radioactively labeled products.34 The preparation of 5-formyl tetrahydrofolate, 9,3, 5 -3H and 5-formyl-14C-tetrahydrofolate starts with tritiated folic acid, which is reduced to dihydrofolate, incubated in the presence of formaldehyde, dihydrofolate reductase, and NADPH, and finally incubated with 5,10-methylenetetrahydrofolate dihydrogenase. The product,... 

Ulrich, C.M., et al., "Pharmacogenetics of Methotrexate Toxicity Among Marrow Transplantation Patients Varies with the Methylenetetrahydrofolate Reductase C677T Polymorphism," Blood, 98, 231-234 (2001). 

Jacques PF, Bostom AG, Williams RR, et al. Relation between folate status, a common mutation in methylenetetrahydrofolate reductase, and plasma homocysteine concentrations. Circulation 1996 93 79. 

Bartoschek, S., Buurman, G., Thauer, R. K., Geierstanger, B. H., Weyrauch, J. P., Griesinger, C., Nilges, M., Hutter, M. C., Helms, V. (2001) Re-face stereospecificity of methylenetetrahy-dromethanopterin dehydrogenases and methylenetetrahydrofolate dehydrogenases is predetermined by intrinsic properties of the substrate. Chem Bio Chem, in press. 

Tysoe, C., Galinsky, D., Robinson, D., et al. (1997) Analysis of alpha-1 antichymotrypsin, presenilin-1, angiotensin-converting enzyme, and methylenetetrahydrofolate reductase loci as candidates for dementia. Am. J. Med. Genet., 74, 207-212. 

Rozen, R. (1996) Molecular genetics of methylenetetrahydrofolate reductase deficiency. Journal of Inherited Metabolic Disease. 19, 589-594. 

Frosst, P., Blom, H.J., Milos, R., et al. (1995) A candidate genetic risk factor for vascular disease a common mutation in methylenetetrahydrofolate reductase. Nature Genetics. 10,111-113. 

Kang, S. S.,Zhou, J., Wong, P.W., Kowalisyn, J., and Strokosch, G. (1988)Intermediate homo-cysteinemia a thermolabile variant of methylenetetrahydrofolate reductase. American Journal of Human Genetics. 43, 414-421. 

Urano, W., Taniguchi, A., Yamanaka, H., et al. (2002) Polymorphisms in the methylenetetrahydrofolate reductase gene were associated with both the efficacy and the toxicity of methotrexate used for the treatment of rheumatoid arthritis, as evidenced by single locus and haplotype analyses. Pharmacogenetics. 12, 183-190. 

Kumagai, K., Hiyama, K., Oyama, T., Maeda, H., and Kohno, N. (2003) Polymorphisms in the thymidylate synthase and methylenetetrahydrofolate reductase genes and sensitivity to the low-dose methotrexate therapy in patients with rheumatoid arthritis. International Journal of Molecular Medicine. 11, 593-600. 

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