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Sah S, Varshney U. Methionyl-tRNA formyltransferase utilizes 10-formyldihydrofolate as an alternative substrate and impacts antifolate drug action. MICROBIOLOGY (READING, ENGLAND) 2023; 169. [PMID: 36745551 DOI: 10.1099/mic.0.001297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Methionyl-tRNA formyltransferase (Fmt)-mediated formylation of Met-tRNAfMet to fMet-tRNAfMet is crucial for efficient initiation of translation in bacteria and the eukaryotic organelles. Folate dehydrogenase-cyclohydrolase (FolD), a bifunctional enzyme, carries out conversion of 5,10-methylene tetrahydrofolate (5,10-CH2-THF) to 10-formyl-THF (10-CHO-THF), a metabolite utilized by Fmt as a formyl group donor. In this study, using in vivo and in vitro approaches, we show that 10-CHO-DHF may also be utilized by Fmt as an alternative substrate (formyl group donor) to formylate Met-tRNAfMet. Dihydrofolate (DHF) formed as a by-product in the in vitro assay was verified by LC-MS/MS analysis. FolD-deficient mutants and Fmt over-expressing strains were more sensitive to trimethoprim (TMP) than the ∆fmt strain, suggesting that the domino effect of TMP leads to inhibition of protein synthesis and strain growth. Antifolate treatment to Escherichia coli showed a decrease in the reduced folate species (THF, 5,10-CH2-THF, 5-CH3-THF, 5,10-CH+-THF and 5-CHO-THF) and increase in the oxidized folate species (folic acid and DHF). In cells, 10-CHO-DHF and 10-CHO-folic acid were enriched in the stationary phase. This suggests that 10-CHO-DHF is a bioactive metabolite in the folate pathway for generating other folate intermediates and fMet-tRNAfMet.
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Affiliation(s)
- Shivjee Sah
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, 560012, India
| | - Umesh Varshney
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, 560012, India
- Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, 560064, India
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Abstract
Preventing the escape of hazardous genes from genetically modified organisms (GMOs) into the environment is one of the most important issues in biotechnology research. Various strategies were developed to create "genetic firewalls" that prevent the leakage of GMOs; however, they were not specially designed to prevent the escape of genes. To address this issue, we developed amino acid (AA)-swapped genetic codes orthogonal to the standard genetic code, namely SL (Ser and Leu were swapped) and SLA genetic codes (Ser, Leu, and Ala were swapped). From mRNAs encoded by the AA-swapped genetic codes, functional proteins were only synthesized in translation systems featuring the corresponding genetic codes. These results clearly demonstrated the orthogonality of the AA-swapped genetic codes against the standard genetic code and their potential to function as "genetic firewalls for genes". Furthermore, we propose "a codon-bypass strategy" to develop a GMO with an AA-swapped genetic code.
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Affiliation(s)
- Tomoshige Fujino
- Department of Biomolecular Engineering, Graduate School of Engineering, Nagoya University, Nagoya, 464-8603, Japan
| | - Masahiro Tozaki
- Department of Biomolecular Engineering, Graduate School of Engineering, Nagoya University, Nagoya, 464-8603, Japan
| | - Hiroshi Murakami
- Department of Biomolecular Engineering, Graduate School of Engineering, Nagoya University, Nagoya, 464-8603, Japan
- Institute of Nano-Life-Systems, Institutes of Innovation for Future Society, Nagoya University, Nagoya, 464-8603, Japan
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Sah S, Shah RA, Govindan A, Varada R, Rex K, Varshney U. Utilisation of 10-formyldihydrofolate as substrate by dihydrofolate reductase (DHFR) and 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) tranformylase/IMP cyclohydrolase (PurH) in Escherichia coli. MICROBIOLOGY-SGM 2019; 164:982-991. [PMID: 29799386 DOI: 10.1099/mic.0.000671] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Dihydrofolate reductase (DHFR) and 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) transformylase/IMP cyclohydrolase (PurH) play key roles in maintaining folate pools in cells, and are targets of antimicrobial and anticancer drugs. While the activities of bacterial DHFR and PurH on their classical substrates (DHF and 10-CHO-THF, respectively) are known, their activities and kinetic properties of utilisation of 10-CHO-DHF are unknown. We have determined the kinetic properties (k cat/K m) of conversion of 10-CHO-DHF to 10-CHO-THF by DHFR, and to DHF by PurH. We show that DHFR utilises 10-CHO-DHF about one third as efficiently as it utilises DHF. The 10-CHO-DHF is also utilised (as a formyl group donor) by PurH albeit slightly less efficiently than 10-CHO-THF. The utilisation of 10-CHO-DHF by DHFR is ~50 fold more efficient than its utilisation by PurH. A folate deficient Escherichia coli (∆pabA) grows well when supplemented with adenine, glycine, thymine and methionine, the metabolites that arise from the one-carbon metabolic pathway. Notably, when the ∆pabA strain harboured a folate transporter, it grew in the presence of 10-CHO-DHF alone, suggesting that it (10-CHO-DHF) can enter one-carbon metabolic pathway to provide the required metabolites. Thus, our studies reveal that both DHFR and PurH could utilise 10-CHO-DHF for folate homeostasis in E. coli.
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Affiliation(s)
- Shivjee Sah
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Riyaz Ahmad Shah
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Ashwin Govindan
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Rajagopal Varada
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Kervin Rex
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Umesh Varshney
- Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064, India.,Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
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Zheng Y, Cantley LC. Toward a better understanding of folate metabolism in health and disease. J Exp Med 2019; 216:253-266. [PMID: 30587505 PMCID: PMC6363433 DOI: 10.1084/jem.20181965] [Citation(s) in RCA: 89] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Revised: 11/18/2018] [Accepted: 12/03/2018] [Indexed: 12/15/2022] Open
Abstract
Folate metabolism is crucial for many biochemical processes, including purine and thymidine monophosphate (dTMP) biosynthesis, mitochondrial protein translation, and methionine regeneration. These biochemical processes in turn support critical cellular functions such as cell proliferation, mitochondrial respiration, and epigenetic regulation. Not surprisingly, abnormal folate metabolism has been causally linked with a myriad of diseases. In this review, we provide a historical perspective, delve into folate chemistry that is often overlooked, and point out various missing links and underdeveloped areas in folate metabolism for future exploration.
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Affiliation(s)
- Yuxiang Zheng
- Department of Medicine, Meyer Cancer Center, Weill Cornell Medicine, New York, NY
| | - Lewis C Cantley
- Department of Medicine, Meyer Cancer Center, Weill Cornell Medicine, New York, NY
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Folate stability and method optimization for folate extraction from seeds of pulse crops using LC-SRM MS. J Food Compost Anal 2018. [DOI: 10.1016/j.jfca.2018.04.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Abstract
Purine nucleotide biosynthesis de novo (PNB) requires 2 folate-dependent transformylases-5'-phosphoribosyl-glycinamide (GAR) and 5'-phosphoribosyl-5-aminoimidazole-4-carboxamide (AICAR) transformylases-to introduce carbon 8 (C8) and carbon 2 (C2) into the purine ring. Both transformylases utilize 10-formyltetrahydrofolate (10-formyl-H4folate), where the formyl-carbon sources include ring-2-C of histidine, 3-C of serine, 2-C of glycine, and formate. Our findings in human studies indicate that glycine provides the carbon for GAR transformylase (exclusively C8), whereas histidine and formate are the predominant carbon sources for AICAR transformylase (C2). Contrary to the previous notion, these carbon sources may not supply a general 10-formyl-H4folate pool, which was believed to equally provide carbons to C8 and C2. To explain these phenomena, we postulate that GAR transformylase is in a complex with the trifunctional folate-metabolizing enzyme (TFM) and serine hydroxymethyltransferase to channel carbons of glycine and serine to C8. There is no evidence for channeling carbons of histidine and formate to AICAR transformylase (C2). GAR transformylase may require the TFM to furnish 10-formyl-H4folate immediately after its production from serine to protect its oxidation to 10-formyldihydrofolate (10-formyl-H2folate), whereas AICAR transformylase can utilize both 10-formyl-H2folate and 10-formyl-H4folate. Human liver may supply AICAR to AICAR transformylase in erythrocytes/erythroblasts. Incorporation of ring-2-C of histidine and formate into C2 of urinary uric acid presented a circadian rhythm with a peak in the morning, which corresponds to the maximum DNA synthesis in the bone marrow, and it may be useful in the timing of the administration of drugs that block PNB for the treatment of cancer and autoimmune disease.
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Affiliation(s)
| | - Tsunenobu Tamura
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL
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Ishizawa T, Kawakami T, Reid PC, Murakami H. TRAP Display: A High-Speed Selection Method for the Generation of Functional Polypeptides. J Am Chem Soc 2013; 135:5433-40. [DOI: 10.1021/ja312579u] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Takahiro Ishizawa
- Department of Life Sciences,
Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Takashi Kawakami
- Department of Life Sciences,
Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Patrick C. Reid
- PeptiDream Inc., 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
| | - Hiroshi Murakami
- Department of Life Sciences,
Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
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Analysis of seven folates in food by LC–MS/MS to improve accuracy of total folate data. Eur Food Res Technol 2012. [DOI: 10.1007/s00217-012-1849-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Pribat A, Noiriel A, Morse AM, Davis JM, Fouquet R, Loizeau K, Ravanel S, Frank W, Haas R, Reski R, Bedair M, Sumner LW, Hanson AD. Nonflowering plants possess a unique folate-dependent phenylalanine hydroxylase that is localized in chloroplasts. THE PLANT CELL 2010; 22:3410-22. [PMID: 20959559 PMCID: PMC2990131 DOI: 10.1105/tpc.110.078824] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Revised: 08/18/2010] [Accepted: 10/05/2010] [Indexed: 05/07/2023]
Abstract
Tetrahydropterin-dependent aromatic amino acid hydroxylases (AAHs) are known from animals and microbes but not plants. A survey of genomes and ESTs revealed AAH-like sequences in gymnosperms, mosses, and algae. Analysis of full-length AAH cDNAs from Pinus taeda, Physcomitrella patens, and Chlamydomonas reinhardtii indicated that the encoded proteins form a distinct clade within the AAH family. These proteins were shown to have Phe hydroxylase activity by functional complementation of an Escherichia coli Tyr auxotroph and by enzyme assays. The P. taeda and P. patens AAHs were specific for Phe, required iron, showed Michaelian kinetics, and were active as monomers. Uniquely, they preferred 10-formyltetrahydrofolate to any physiological tetrahydropterin as cofactor and, consistent with preferring a folate cofactor, retained activity in complementation tests with tetrahydropterin-depleted E. coli host strains. Targeting assays in Arabidopsis thaliana mesophyll protoplasts using green fluorescent protein fusions, and import assays with purified Pisum sativum chloroplasts, indicated chloroplastic localization. Targeting assays further indicated that pterin-4a-carbinolamine dehydratase, which regenerates the AAH cofactor, is also chloroplastic. Ablating the single AAH gene in P. patens caused accumulation of Phe and caffeic acid esters. These data show that nonflowering plants have functional plastidial AAHs, establish an unprecedented electron donor role for a folate, and uncover a novel link between folate and aromatic metabolism.
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Affiliation(s)
- Anne Pribat
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611
| | - Alexandre Noiriel
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611
| | - Alison M. Morse
- School of Forest Resources and Conservation, University of Florida, Gainesville, Florida 32611
| | - John M. Davis
- School of Forest Resources and Conservation, University of Florida, Gainesville, Florida 32611
| | - Romain Fouquet
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611
| | - Karen Loizeau
- Laboratoire de Physiologie Cellulaire Végétale, Centre National de la Recherche Scientifique/Commissariat à l’Energie Atomique/Institut National de la Recherche Agronomique/Université Joseph Fourier, Commissariat à l’Energie Atomique-Grenoble, F-38054 Grenoble Cedex 9, France
| | - Stéphane Ravanel
- Laboratoire de Physiologie Cellulaire Végétale, Centre National de la Recherche Scientifique/Commissariat à l’Energie Atomique/Institut National de la Recherche Agronomique/Université Joseph Fourier, Commissariat à l’Energie Atomique-Grenoble, F-38054 Grenoble Cedex 9, France
| | - Wolfgang Frank
- Plant Biotechnology, Faculty of Biology, University of Freiburg, D-79104 Freiburg, Germany
| | - Richard Haas
- Plant Biotechnology, Faculty of Biology, University of Freiburg, D-79104 Freiburg, Germany
| | - Ralf Reski
- Plant Biotechnology, Faculty of Biology, University of Freiburg, D-79104 Freiburg, Germany
| | - Mohamed Bedair
- Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401
| | - Lloyd W. Sumner
- Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401
| | - Andrew D. Hanson
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611
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Baggott JE, Tamura T. Evidence for the hypothesis that 10-formyldihydrofolate is the in vivo substrate for aminoimidazolecarboxamide ribotide transformylase. Exp Biol Med (Maywood) 2010; 235:271-7. [PMID: 20404044 DOI: 10.1258/ebm.2009.009151] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We postulate that 10-formyl-7,8-dihydrofolate (10-HCO-H(2)folate), not 10-formyl-5,6,7,8-tetrahydrofolate (10-HCO-H(4)folate), is the predominant in vivo substrate for mammalian aminoimidazolecarboxamide ribotide (AICAR) transformylase, an enzyme in purine nucleotide biosynthesis de novo, which introduces carbon 2 (C(2)) into the purine ring. 10-HCO-H(2)folate exists in vivo as labeled 10-formyl-folic acid (10-HCO-folic acid: an oxidation product of 10-HCO-H(4)folate and 10-HCO-H(2)folate) and is found after doses of labeled folic acid in humans or laboratory animals. The bioactivity of the unnatural isomer, [6R]-5-formyltetrahydrofolate, in humans is explained by its in vivo conversion to 10-HCO-H(2)folate. The structure and active site of AICAR transformylase are not consistent with other enzymes that utilize 10-HCO-H(4)folate. Because 10-HCO-H(4)folate is rapidly oxidized in vitro to 10-HCO-H(2)folate by cytochrome C alone and in mitochondria, it is hypothesized that this process takes place in vivo. In vitro data indicate that 10-HCO-H(2)folate is kinetically preferred over 10-HCO-H(4)folate by AICAR transformylase and that this enzyme may not have access to sufficient supplies of 10-HCO-H(4)folate. Methotrexate blockage of the AICAR transformylase process in patients with rheumatoid arthritis suggests that dihydrofolate (H(2)folate) reductase is involved and is consistent with H(2)folate and 10-HCO-H(2)folate being the product and substrate for AICAR transformylase. The labeling of purine C(2) by an oral dose of [6RS]-5-H[(13)C]O-H(4)folate in a human subject is consistent with 10-H[(13)C]O-H(2)folate formation from unnatural isomer, [6R]-5-H[(13)C]O-H(4)folate, and it being a substrate for AICAR transformylase. In vitro exchange reactions of purine C(2) using H(4)folate coenzymes are not duplicated in vivo and is consistent with H(2)folate coenzymes being used in vivo by AICAR transformylase.
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Affiliation(s)
- Joseph E Baggott
- Department of Nutrition Sciences, University of Alabama at Birmingham, 35294, USA
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12
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Tyagi A, Penzkofer A, Batschauer A, Wolf E. Fluorescence behaviour of 5,10-methenyltetrahydrofolate, 10-formyltetrahydrofolate, 10-formyldihydrofolate, and 10-formylfolate in aqueous solution at pH 8. Chem Phys 2009. [DOI: 10.1016/j.chemphys.2009.05.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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13
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Tyagi A, Penzkofer A, Batschauer A, Wolf E. Thermal degradation of (6R,S)-5,10-methenyltetrahydrofolate in aqueous solution at pH 8. Chem Phys 2009. [DOI: 10.1016/j.chemphys.2009.01.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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14
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Absorption and fluorescence spectroscopic characterisation of the circadian blue-light photoreceptor cryptochrome from Drosophila melanogaster (dCry). Chem Phys 2008. [DOI: 10.1016/j.chemphys.2008.06.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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15
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Baggott JE, Gorman GS, Morgan SL, Tamura T. 13C-enrichment at carbons 8 and 2 of uric acid after 13C-labeled folate dose in man. Biochem Biophys Res Commun 2007; 361:307-10. [PMID: 17643394 PMCID: PMC2151848 DOI: 10.1016/j.bbrc.2007.06.133] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2007] [Accepted: 06/26/2007] [Indexed: 11/23/2022]
Abstract
To evaluate folate-dependent carbon incorporation into the purine ring, we measured (13)C-enrichment independently at C(2) and C(8) of urinary uric acid (the final catabolite of purines) in a healthy male after an independent oral dose of [6RS]-5-[(13)C]-formyltetrahydrofolate ([6RS]-5-H(13)CO-H(4)folate) or 10-H(13)CO-7,8-dihydrofolate (10-H(13)CO-H(2)folate). The C(2) position was (13)C-enriched more than C(8) after [6RS]-5-H(13)CO-H(4)folate, and C(2) was exclusively enriched after 10-H(13)CO-H(2)folate. The enrichment of C(2) was greater from [6RS]-5-H(13)CO-H(4)folate than 10-H(13)CO-H(2)folate using equimolar bioactive doses. Our data suggest that formyl C of [6RS]-10-H(13)CO-H(4)folate was not equally utilized by glycinamide ribotide transformylase (enriches C(8)) and aminoimidazolecarboxamide ribotide (AICAR) transformylase (enriches C(2)), and the formyl C of 10-H(13)CO-H(2)folate was exclusively used by AICAR transformylase. 10-HCO-H(2)folate may function in vivo as the predominant substrate for AICAR transformylase in humans.
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Affiliation(s)
- Joseph E Baggott
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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Goyer A, Collakova E, Díaz de la Garza R, Quinlivan EP, Williamson J, Gregory JF, Shachar-Hill Y, Hanson AD. 5-Formyltetrahydrofolate Is an Inhibitory but Well Tolerated Metabolite in Arabidopsis Leaves. J Biol Chem 2005; 280:26137-42. [PMID: 15888445 DOI: 10.1074/jbc.m503106200] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
5-Formyltetrahydrofolate (5-CHO-THF) is formed via a second catalytic activity of serine hydroxymethyltransferase (SHMT) and strongly inhibits SHMT and other folate-dependent enzymes in vitro. The only enzyme known to metabolize 5-CHO-THF is 5-CHO-THF cycloligase (5-FCL), which catalyzes its conversion to 5,10-methenyltetrahydrofolate. Because 5-FCL is mitochondrial in plants and mitochondrial SHMT is central to photorespiration, we examined the impact of an insertional mutation in the Arabidopsis 5-FCL gene (At5g13050) under photorespiratory (30 and 370 micromol of CO2 mol(-1)) and non-photorespiratory (3200 micromol of CO2 mol(-1)) conditions. The mutation had only mild visible effects at 370 micromol of CO2 mol(-1), reducing growth rate by approximately 20% and delaying flowering by 1 week. However, the mutation doubled leaf 5-CHO-THF level under all conditions and, under photorespiratory conditions, quadrupled the pool of 10-formyl-/5,10-methenyltetrahydrofolates (which could not be distinguished analytically). At 370 micromol of CO2 mol(-1), the mitochondrial 5-CHO-THF pool was 8-fold larger in the mutant and contained most of the 5-CHO-THF in the leaf. In contrast, the buildup of 10-formyl-/5,10-methenyltetrahydrofolates was extramitochondrial. In photorespiratory conditions, leaf glycine levels were up to 46-fold higher in the mutant than in the wild type. Furthermore, when leaves were supplied with 5-CHO-THF, glycine accumulated in both wild type and mutant. These data establish that 5-CHO-THF can inhibit SHMT in vivo and thereby influence glycine pool size. However, the near-normal growth of the mutant shows that even exceptionally high 5-CHO-THF levels do not much affect fluxes through SHMT or any other folate-dependent reaction, i.e. that 5-CHO-THF is well tolerated in plants.
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Affiliation(s)
- Aymeric Goyer
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611, USA
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17
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Telegina TA, Lyudnikova TA, Zemskova YL, Sviridov EA, Kritsky MS. Resistance of 5,10-methenyltetrahydrofolate to ultraviolet radiation. APPL BIOCHEM MICRO+ 2005. [DOI: 10.1007/s10438-005-0047-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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18
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Kariluoto S, Vahteristo L, Salovaara H, Katina K, Liukkonen KH, Piironen V. Effect of Baking Method and Fermentation on Folate Content of Rye and Wheat Breads. Cereal Chem 2004. [DOI: 10.1094/cchem.2004.81.1.134] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Susanna Kariluoto
- Viikki Food Science, Department of Applied Chemistry and Microbiology, P.O.Box 27, FIN-00014, University of Helsinki, Finland
- Corresponding author. Phone: 358-9-191-58252. E-mail:
| | - Liisa Vahteristo
- Viikki Food Science, Department of Applied Chemistry and Microbiology, P.O.Box 27, FIN-00014, University of Helsinki, Finland
| | - Hannu Salovaara
- Viikki Food Science, Department of Cereal Technology, P.O.Box 27, FIN-00014 University of Helsinki, Finland
| | - Kati Katina
- VTT Biotechnology, P.O.Box 1500, FIN-02044 VTT, Finland
| | | | - Vieno Piironen
- Viikki Food Science, Department of Applied Chemistry and Microbiology, P.O.Box 27, FIN-00014, University of Helsinki, Finland
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Brookes PS, Baggott JE. Oxidation of 10-formyltetrahydrofolate to 10-formyldihydrofolate by complex IV of rat mitochondria. Biochemistry 2002; 41:5633-6. [PMID: 11969424 DOI: 10.1021/bi0120244] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We hypothesized that the unanticipated bioactivity of orally administered unnatural carbon-6 isomers, (6R)-5-formyltetrahydrofolate (5-HCO-THF) and (6S)-5,10-methenyltetrahydrofolate (5,10-CH-THF), in humans [Baggott, J. E., and Tamura, T. (1999) Biochim. Biophys. Acta 1472, 323-32] is explained by the rapid oxidation of (6S)-10-formyltetrahydrofolate (10-HCO-THF), which is produced by in vivo chemical processes from the above folates. An oxidation of 10-HCO-THF produces 10-formyldihydrofolate (10-HCO-DHF), which no longer has the asymmetric center at carbon-6 and is metabolized by aminoimidazole carboxamide ribotide (AICAR) transformylase forming bioactive dihydrofolate. Since cytochrome c (Fe(3+)) rapidly oxidizes both (6R)- and (6S)-10-HCO-THF [Baggott et al. (2001) Biochem. J. 354, 115-22], we investigated the metabolism of 10-HCO-THF by isolated rat liver mitochondria. We found that 10-HCO-THF supported the respiration of mitochondria without uncoupling ATP synthesis. The site of electron donation was identified as complex IV, which contains cytochrome c; the folate product was 10-HCO-DHF, and the reaction was saturable with respect to 10-HCO-THF. Both (6S)- (unnatural) and (6R)-10-HCO-THF supported the respiration of mitochondria, whereas (6S)-5-formyltetrahydrofolate (5-HCO-THF) was inactive. To our knowledge, this cytochrome c oxidation of 10-HCO-THF to 10-HCO-DHF in the mitochondrial intermembrane space represents a possible folate metabolic pathway previously unidentified and would explain the bioactivity of unnatural carbon-6 isomers, (6R)-5-HCO-THF and (6S)-5,10-CH-THF, in humans.
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Affiliation(s)
- Paul S Brookes
- Department of Pathology and Department of Nutrition Sciences, University of Alabama at Birmingham, 35294, USA
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Abstract
The metabolism of 10-formyldihydrofolate is reviewed in this article. It had been the dogma that only tetrahydrofolates participate in enzyme-catalyzed one-carbon transfer reactions, until we showed in 1986 that 10-formyldihydrofolate serves as a substrate for aminoimidazolecarboxamide ribotide (AICAR) transformylase. Our data from studies in humans, cultured cells and bacteria as well as in vitro experiments indicate that the oxidation of 10-formyltetrahydrofolate to 10-formyldihydrofolate takes place, and 1 0-formyldihydrofolate is subsequently converted to dihydrofolate by AICAR transformylase. Dihydrofolate is then reduced to tetrahydrofolate and further metabolized by the well-established enzyme reactions. We believe that a new folate metabolic map is needed which incorporates the oxidation of 10-formyltetrahydrofolate and the utilization of 10-formyldihydrofolate by AICAR transformylase.
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Affiliation(s)
- J E Baggott
- Department of Nutrition Sciences, University of Alabama at Birmingham, 35294-3360, USA.
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Baggott JE, Tamura T, Baker H. Re-evaluation of the metabolism of oral doses of racemic carbon-6 isomers of formyltetrahydrofolate in human subjects. Br J Nutr 2001; 85:653-7. [PMID: 11430769 DOI: 10.1079/bjn2001323] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The racemic mixture, [6RS]-5-formyltetrahydrofolate, is widely used clinically. In human subjects, orally-administered pure unnatural C-6 isomers, [6R]-5-formyltetrahydrofolate and [6S]-5,10-methenyltetrahydrofolate, were recently shown to be metabolized to the natural isomer, [6S]-5-methyltetrahydrofolate. We re-analysed the data from human studies published during the past four decades in which oral doses (< or =10 mg) of racemic mixtures of these folates were used. We re-evaluated the data to determine whether these racemic mixtures are only 50 % bioactive or, as we now predict, more than 50 % bioactive. Our analyses indicate that, in human subjects, oral doses of the racemic mixture of the two formyltetrahydrofolates are 20-84 % more bioactive than would be predicted. These data are consistent with the following pathway: chemical conversion of these folates to 10-formyltetrahydrofolate; oxidation of 10-formyltetrahydrofolate to 10-formyldihydrofolate; subsequent enzymic conversion of 10-formyldihydrofolate to dihydrofolate by 5-amino-4-imidazolecarboxamide ribotide transformylase; and finally the well-established metabolism of dihydrofolate to [6S]-5-methyltetrahydrofolate. An additional review of the literature supports the in vivo oxidation of 10-formyltetrahydrofolate occurring to a certain extent, as 10-formyl-folic acid is rapidly formed after the administration of folic acid (pteroylglutamic acid) or 5-formyltetrahydrofolate in human subjects. The dogma that an oral dose of the unnatural C-6 isomer of 5-formyltetrahydrofolate is not bioactive in human subjects does not withstand scrutiny, most probably due to the previously unrecognized in vivo oxidation of 10-formyltetrahydrofolate. This discovery unveils new folate metabolism in human subjects.
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Affiliation(s)
- J E Baggott
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
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22
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Baggott JE, Robinson CB, Johnston KE. Bioactivity of [6R]-5-formyltetrahydrofolate, an unusual isomer, in humans and Enterococcus hirae, and cytochrome c oxidation of 10-formytetrahydrofolate to 10-formyldihydrofolate. Biochem J 2001; 354:115-22. [PMID: 11171086 PMCID: PMC1221635 DOI: 10.1042/0264-6021:3540115] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The bio-inactive C-6 isomer, [6R]-5-formyl-tetrahydrofolate (5-HCO-H(4)F), is not found in Nature. An oral dose of 13.5 micromol of [6R]-5-HCO-H(4)F in humans results in the appearance of the naturally occurring [6S]-5-methyl-tetrahydrofolate and relatively large amounts of other bioactive folates in plasma. The removal of the asymmetry at C-6 could account for these results. Two oxidized cytochrome c [cyt c (Fe3+)] molecules oxidize one 10-formyl-tetrahydrofolate (10-HCO-H(4)F) with second-order kinetics and a rate constant of 1.3 x 10(4) M(-1) x s(-1). The folate product of this oxidation reaction is 10-formyl-dihydrofolate (10-HCO-H(2)F), which has no C-6 asymmetric centre and is therefore bioactive. The folate-requiring bacterium, Enterococcus hirae, does not normally biosynthesize cytochromes but does so when given an exogenous source of haem (e.g. haemin). E. hirae grown in haemin-supplemented media for 3 days utilizes both [6R]- and [6S]-5-HCO-H(4)F in contrast to that grown in control medium, which utilizes only the [6S] isomer. Since known chemical reactions form 10-HCO-H(4)F from 5-HCO-H(4)F, the unusually large rate constant for the oxidation of 10-HCO-H(4)F by cyt c (Fe3+) may account for the unexpected bioactivity of [6R]-5-HCO-H(4)F in humans and in E. hirae grown in haemin-containing media. We used an unnatural C-6 folate isomer as a tool to reveal the possible in vivo oxidation of 10-HCO-H(4)F to 10-HCO-H(2)F; however, nothing precludes this oxidation from occurring in vivo with the natural C-6 isomer.
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Affiliation(s)
- J E Baggott
- Department of Nutrition Sciences, 336 Webb Building, 1675 University Blvd., University of Alabama at Birmingham, Birmingham, AL 35294-3360, USA.
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Baggott JE. Hydrolysis of 5,10-methenyltetrahydrofolate to 5-formyltetrahydrofolate at pH 2.5 to 4.5. Biochemistry 2000; 39:14647-53. [PMID: 11087421 DOI: 10.1021/bi001362m] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
At pH 4.0 to 4.5, 5,10-methenyltetrahydrofolate is hydrolyzed to only 5-formyltetrahydrofolate if reducing agents are present or iron-redox cycling is suppressed. At pH 4.0, the equilibrium position for this hydrolysis is approximately equal concentrations of both folates. If no reducing agents are used or iron-redox cycling is promoted, considerable amounts of 10-formyldihydrofolate are also formed. It is likely that 10-formyldihydrofolate has been misidentified as 5,10-hydroxymethylenetetrahydrofolate, which was reported to accumulate during the hydrolysis of 5, 10-methenyltetrahydrofolate to 5-formyltetrahydrofolate [Stover, P. and Schirch, V. (1992) Biochemistry 31, 2148-2155 and 2155-2164; (1990) J. Biol. Chem. 265, 14227-14233]. Since 5, 10-hydroxymethylenetetrahydrofolate is reported to be the viable in vivo substrate for serine hydroxymethyltransferase-catalyzed formation of 5-formyltetrahydrofolate, and 5, 10-hydroxymethylenetetrahydrofolate probably does not accumulate, the above folate metabolism is now doubtful. It is hypothesized that mildly acidic subcellular organelles provide an environment for the hydrolysis of 5,10-methenyltetrahydrofolate to 5-formyltetrahydrofolate in vivo, and there is no requirement for enzyme catalysis. Finally, 10-formyltetrahydrofolate is susceptible to iron-catalyzed oxidation to 10-formyldihydrofolate at pH 4 to 4.5.
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Affiliation(s)
- J E Baggott
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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Wall M, Shim JH, Benkovic SJ. Human AICAR transformylase: role of the 4-carboxamide of AICAR in binding and catalysis. Biochemistry 2000; 39:11303-11. [PMID: 10985775 DOI: 10.1021/bi0007268] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have prepared 4-substituted analogues of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) to investigate the specificity and mechanism of AICAR transformylase (AICAR Tfase). Of the nine analogues of AICAR studied, only one analogue, 5-aminoimidazole-4-thiocarboxamide ribonucleotide, was a substrate, and it was converted to 6-mercaptopurine ribonucleotide. The other analogues either did not bind or were competitive inhibitors, the most potent being 5-amino-4-nitroimidazole ribonucleotide with a K(i) of 0.7 +/- 0.5 microM. The results show that the 4-carboxamide of AICAR is essential for catalysis, and it is proposed to assist in mediating proton transfer, catalyzing the reaction by trapping of the addition compound. AICAR analogues where the nitrogen of the 4-carboxamide was derivatized with a methyl or an allylic group did not bind AICAR Tfase, as determined by pre-steady-state burst kinetics; however, these compounds were potent inhibitors of IMP cyclohydrolase (IMP CHase), a second activity of the bifunctional mammalian enzyme (K(i) = 0.05 +/- 0.02 microM for 4-N-allyl-AlCAR). It is proposed that the conformation of the carboxamide moiety required for binding to AICAR Tfase is different than the conformation required for binding to IMP CHase, which is supported by inhibition studies of purine ribonucleotides. It is shown that 5-formyl-AICAR (FAICAR) is a product inhibitor of AICAR Tfase with K(i) of 0.4 +/- 0.1 microM. We have determined the equilibrium constant of the transformylase reaction to be 0.024 +/- 0.001, showing that the reaction strongly favors AICAR and the 10-formyl-folate cofactor. The coupling of the AICAR Tfase and IMP CHase activities on a single polypeptide allows the overall conversion of AICAR to IMP to be favorable by coupling the unfavorable formation of FAICAR with the highly favorable cyclization reaction. The current kinetic studies have also indicated that the release of FAICAR is the rate-limiting step, under steady-state conditions, in the bifunctional enzyme and channeling is not observed between AICAR Tfase and IMP CHase.
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Affiliation(s)
- M Wall
- Department of Chemistry, 415 Wartik Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Hong KH, Keen CL, Mizuno Y, Johnston KE, Tamura T. Effects of dietary zinc deficiency on homocysteine and folate metabolism in rats. J Nutr Biochem 2000; 11:165-9. [PMID: 10742662 DOI: 10.1016/s0955-2863(99)00089-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
In rats, zinc deficiency has been reported to result in elevated hepatic methionine synthase activity and alterations in folate metabolism. We investigated the effect of zinc deficiency on plasma homocysteine concentrations and the distribution of hepatic folates. Weanling male rats were fed ad libitum a zinc-sufficient control diet (382.0 nmol zinc/g diet), a low-zinc diet (7.5 nmol zinc/g diet), or a control diet pair-fed to the intake of the zinc-deficient rats. After 6 weeks, the body weights of the zinc-deficient and pair-fed control groups were lower than those of controls, and plasma zinc concentrations were lowest in the zinc-deficient group. Plasma homocysteine concentrations in the zinc-deficient group (2.3 +/- 0.2 micromol/L) were significantly lower than those in the ad libitum-fed and pair-fed control groups (6.7 +/- 0.5 and 3.2 +/- 0.4 micromol/L, respectively). Hepatic methionine synthase activity in the zinc-deficient group was higher than in the other two groups. Low mean percentage of 5-methyltetrahydrofolate in total hepatic folates and low plasma folate concentration were observed in the zinc-deficient group compared with the ad libitum-fed and pair-fed control groups. The reduced plasma homocysteine and folate concentrations and reduced percentage of hepatic 5-methyltetrahydrofolate are probably secondary to the increased activity of hepatic methionine synthase in zinc deficiency.
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Affiliation(s)
- K H Hong
- Department of Nutrition, University of California, Davis, CA, USA
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Baggott JE, Tamura T. Bioactivity of orally administered unnatural isomers, [6R]-5-formyltetrahydrofolate and [6S]-5,10-methenyltetrahydrofolate, in humans. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1472:323-32. [PMID: 10572954 DOI: 10.1016/s0304-4165(99)00135-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
It has been assumed that humans cannot utilize 5,6,7,8-tetrahydrofolates with the unnatural configuration at carbon 6, since these folates are enzymatically and microbiologically inactive. We hypothesized that orally administered unnatural [6R]-5-formyltetrahydrofolate or [6S]-5,10-methenyltetrahydrofolate is bioactive in humans. Subjects were given independent oral doses of these unnatural folates and of a natural [6S]-5-formyltetrahydrofolate. Plasma, before and after the dose for 4 h, and 2 h urine were collected. Areas under the curve for the change in plasma folate concentrations were measured microbiologically and urinary folates were measured using HPLC. Based on findings of plasma and urinary folates, the unnatural folates were estimated to be 14-50% active as compared to [6S]-5-formyltetrahydrofolate. The major plasma and urinary folate was [6S]-5-methyltetrahydrofolate in all experiments. In urine, a [6S]-5-formyltetrahydrofolate peak was observed only after a [6S]-5-HCO-H4folate dose and peaks of unnatural [6S]-10-formyltetrahydrofolate and 5-formyltetrahydrofolate were identified after a [6R]-5-formyltetrahydrofolate dose. A possible pathway that explains our findings is discussed. This pathway includes the oxidation of the unnatural [6S]-10-formyltetrahydrofolate to 10-formyl-7,8-dihydrofolate which can be further metabolized by 5-amino-4-imidazolecarboxamide-ribotide transformylase producing dihydrofolate. Dihydrofolate can then be metabolized to [6S]-5-methyltetrahydrofolate by well-established metabolism.
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Affiliation(s)
- J E Baggott
- Department of Nutrition Sciences, University of Alabama at Birmingham, 35294-3360, USA
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Abstract
The bioactivity of 10-formyl-7,8-dihydrofolic acid and 10-formyl-folic acid was determined in human leukemia (CCRF-CEM) cells grown in a folate-depleted medium containing methotrexate. Excess 10-formyl-7,8-dihydrofolic acid, (but not 10-formyl folic acid) supported the growth of these cells, but it was less potent than5-formyl-5,6,7,8-tetrahydrofolic acid (a control). 10-formyl-7, 8-dihydrofolic acid (not 10-formyl folic acid) was active as substrate for aminoimidazole carboxamide ribotide transformylase and dihydrofolate reductase. This is the first experimental evidence that 10-formyl-7,8-dihydrofolic acid is a bioactive folate in mammalian cells. These experiments and several other lines of evidence in the literature suggest that 10-formyl-folic acid must be metabolized to bioactive folate by enteric bacteria before it can be utilized by the vertebrate host.
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Affiliation(s)
- J E Baggott
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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Tamura T, Hong KH, Mizuno Y, Johnston KE, Keen CL. Folate and homocysteine metabolism in copper-deficient rats. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1427:351-6. [PMID: 10350650 DOI: 10.1016/s0304-4165(99)00043-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
To investigate the effect of copper deficiency on folate and homocysteine metabolism, we measured plasma, red-cell and hepatic folate, plasma homocysteine and vitamin B-12 concentrations, and hepatic methionine synthase activities in rats. Two groups of male Sprague-Dawley rats were fed semi-purified diets containing either 0. 1 mg (copper-deficient group) or 9.2 mg (control group) of copper per kg. After 6 weeks of dietary treatment, copper deficiency was established as evidenced by markedly decreased plasma and hepatic copper concentrations in rats fed the low-copper diet. Plasma, red-cell, hepatic folate, and plasma vitamin B-12 concentrations were similar in both groups, whereas plasma homocysteine concentrations in the copper-deficient group were significantly higher than in the control group (P<0.05). Copper deficiency resulted in a 21% reduction in hepatic methionine synthase activity as compared to the control group (P<0.01). This change most likely caused the increased hepatic 5-methyltetrahydrofolate and plasma homocysteine concentrations in the copper-deficient group. Our results indicate that hepatic methionine synthase may be a cuproenzyme, and plasma homocysteine concentrations are influenced by copper nutriture in rats. These data support the concept that copper deficiency can be a risk factor for cardiovascular disease.
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Affiliation(s)
- T Tamura
- Department of Nutrition Sciences, 218 Webb Bldg., University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
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Baggott JE, Robinson CB, Eto I, Johanning GL, Cornwell PE. Iron compounds catalyze the oxidation of 10-formyl-5,6,7,8 tetrahydrofolic acid to 10-formyl-7,8 dihydrofolic acid. J Inorg Biochem 1998; 71:181-7. [PMID: 9833324 DOI: 10.1016/s0162-0134(98)10052-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have previously demonstrated that 10-formyl-7,8-dihydrofolic acid (10-HCO-H2folate) is a better substrate for mammalian aminoimidazolecarboxamide ribotide transformylase (EC 2.1.2.3) than is 10-formyl-5,6,7,8-tetrahydrofolic acid (10-HCO-H4folate) (J.E. Baggott, G.L. Johanning, K.E. Branham, C.W. Prince, S.L. Morgan, I. Eto, W.H. Vaughn, Biochem. J. 308, 1995, 1031-1036). Therefore, the possible metabolism of 10-HCO-H4folate to 10-HCO-H2folate was investigated. A spectrophotometric assay for the oxidation of 10-HCO-H4folate to 10-HCO-H2folate which measures the disappearance of reactant (decrease in absorbance at 356 nm after acidification of aliquots of the reaction solution), is used to demonstrate that iron compounds catalyze the oxidation of 10-HCO-H4folate to 10-HCO-H2folate in the presence and absence of ascorbate. Chromatographic separation of the 10-HCO-H2folate product from the reaction mixture, its UV spectra, a microbiological assay and an enzymatic assay established that the iron-catalyzed oxidation product of 10-HCO-H4folate was 10-HCO-H2folate; without substantial side reactions. The inhibition of this iron-catalyzed oxidation by deferoxamine, apotransferrin and mannitol and the stimulation by citrate and EDTA indicated of a mechanism involving a reaction of 10-HCO-H4folate with hydroxyl radicals (*OH) generated by Fenton chemistry. The presence of "free iron" (e.g., Fe3+ citrate) in bile, cerebrospinal fluid and intracellularly suggest that this oxidation could occur in vivo and that 10-HCO-H4folate may be a *OH scavenger.
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Affiliation(s)
- J E Baggott
- Department of Nutrition Sciences, School of Health Related Professions, University of Alabama at Birmingham 35294, USA
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Baggott JE, Morgan SL, Koopman WJ. The effect of methotrexate and 7-hydroxymethotrexate on rat adjuvant arthritis and on urinary aminoimidazole carboxamide excretion. ARTHRITIS AND RHEUMATISM 1998; 41:1407-10. [PMID: 9704638 DOI: 10.1002/1529-0131(199808)41:8<1407::aid-art9>3.0.co;2-h] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
OBJECTIVE To study the efficacy, toxicity, and antifolate activities of 7-hydroxymethotrexate (7-OH-MTX) versus methotrexate (MTX) in the treatment of rat adjuvant-induced arthritis. METHODS Dose-dependent effects in rat adjuvant arthritis were determined by histologic and clinical examinations. Antifolate activity was determined by urinary levels of aminoimidazole carboxamide (AIC) as a marker for blockade of the folate-dependent enzyme, aminoimidazolecarboxamide ribotide transformylase (AICARTase). RESULTS MTX was 8 times more efficacious than 7-OH-MTX and resulted in higher urinary AIC levels. Increased urinary AIC levels were correlated with suppression of rat adjuvant arthritis regardless of the drug or dose level used. CONCLUSION The ability to metabolize MTX to 7-OH-MTX and the sensitivity of AICARTase to inhibition by 7-OH-MTX may at least partially account for the variability in response to MTX. Blocking of AICARTase may be important in the efficacy of these antifolates.
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Affiliation(s)
- J E Baggott
- University of Alabama at Birmingham, 35294, USA
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