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Results: 11 to 20 of 21

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The utilization of formate by human erythrocytes.
Wagner C, Levitch ME
(1973) Biochim Biophys Acta 304: 623-33
MeSH Terms: Alcohol Oxidoreductases, Biological Assay, Carbon Isotopes, Erythrocytes, Folic Acid, Formates, Homocysteine, Humans, Imidazoles, Lactobacillus, Ligases, Methyltransferases, Oxidoreductases, Streptomyces, Tetrahydrofolates, Transferases
Added January 20, 2015
0 Communities
1 Members
0 Resources
16 MeSH Terms
Inhibition of glycine N-methyltransferase activity by folate derivatives: implications for regulation of methyl group metabolism.
Wagner C, Briggs WT, Cook RJ
(1985) Biochem Biophys Res Commun 127: 746-52
MeSH Terms: Animals, Binding, Competitive, Folic Acid, Glycine N-Methyltransferase, Male, Methyltransferases, Pteroylpolyglutamic Acids, Rats, Rats, Inbred Strains, Tetrahydrofolates
Show Abstract · Added January 20, 2015
Glycine N-methyltransferase, an enzyme that uses S-adenosylmethionine to methylate glycine with the production of sarcosine, was recently shown to be identical with a major folate binding protein of rat liver (Cook, R.J. and Wagner, C. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 3631-3634). We now present evidence that 5-methyltetrahydropteroylpentaglutamate (5-CH3-H4PteGlu5) is bound with high specificity, and is a powerful inhibitor of the enzyme. It is proposed that this information may be used to modify the "methyl trap" hypothesis which describes how the availability of one-carbon units is regulated by folate, vitamin B12 and methionine.
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10 MeSH Terms
Effect of dietary methyl group deficiency on folate metabolism in rats.
Horne DW, Cook RJ, Wagner C
(1989) J Nutr 119: 618-21
MeSH Terms: Amino Acids, Animals, Choline Deficiency, Chromatography, High Pressure Liquid, Diet, Folic Acid, Leucovorin, Liver, Male, Methionine, Methylation, Rats, Rats, Inbred F344, Tetrahydrofolates
Show Abstract · Added January 20, 2015
The carcinogenic effects of methyl-deficient, amino acid-defined diets have been attributed to alterations in cellular methylation reactions. These diets contain no choline, and methionine is replaced by homocysteine. Hence, all methyl groups needed for methionine biosynthesis with subsequent formation of S-adenosylmethionine and polyamines must be formed de novo utilizing folate-dependent reduction of one-carbon units. In rats fed the methyl-deficient diet, there was a marked decrease in total liver folate levels. This decrease was apparent in the levels of the individual forms of folate: 10-HCO-H4folate, 5-HCO-H4folate, 5-CH3-H4folate and H4folate. The percent of the total folate pool made up by 5-CH3-H4folate did not change, however, until after the rats had been fed the methyl-deficient diet for 4 wk, and then an increase was seen. After the methyl-deficient rats were switched to a nutritionally adequate control diet containing methionine and choline, all values rapidly reversed. Increased use of folate for methyl group biosynthesis may be responsible for the loss of folates from the liver.
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14 MeSH Terms
Phosphorylation modulates the activity of glycine N-methyltransferase, a folate binding protein. In vitro phosphorylation is inhibited by the natural folate ligand.
Wagner C, Decha-Umphai W, Corbin J
(1989) J Biol Chem 264: 9638-42
MeSH Terms: Animals, Carrier Proteins, Enzyme Activation, Folate Receptors, GPI-Anchored, Folic Acid, Glycine N-Methyltransferase, Liver, Male, Methyltransferases, Phosphates, Phosphorylation, Protein Kinases, Rats, Receptors, Cell Surface, Substrate Specificity, Tetrahydrofolates
Show Abstract · Added January 20, 2015
Glycine N-methyltransferase (EC 2.1.1.20) was recently identified as a major folate binding protein of rat liver cytosol (Wagner, C., and Cook, R. J. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 3631-3634). Activity of the enzyme is inhibited when the natural folate ligand, 5-methyltetrahydropteroylpentaglutamate (5-CH3-H4PteGlu5), is bound. It has been suggested that glycine N-methyltransferase plays a role in regulating the availability of methyl groups in the liver. Purified transferase was phosphorylated in vitro by the catalytic subunit of cAMP-dependent protein kinase. If 5-CH3-H4PteGlu5 was first bound to the transferase, phosphorylation was inhibited. Phosphorylation of glycine N-methyltransferase in vitro increased its activity approximately 2-fold. 5-CH3-H4PteGlu5 inhibited the activity of newly phosphorylated enzyme as well as native enzyme. Freshly isolated rat hepatocytes incorporated 32P-labeled inorganic phosphate into this folate binding protein. Chemical analysis of purified enzyme showed about 0.55 mol of phosphate present per mol of glycine N-methyltransferase subunit. These results indicate that phosphorylation of glycine N-methyltransferase may provide a mechanism for modulating the activity of this enzyme and support its role in regulating the availability of methyl groups.
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16 MeSH Terms
Enzymatic properties of dimethylglycine dehydrogenase and sarcosine dehydrogenase from rat liver.
Porter DH, Cook RJ, Wagner C
(1985) Arch Biochem Biophys 243: 396-407
MeSH Terms: Anaerobiosis, Animals, Chromatography, High Pressure Liquid, Chromatography, Ion Exchange, Dimethylglycine Dehydrogenase, Enzyme Activation, Formaldehyde, Glycine, Kinetics, Mathematics, Mitochondria, Liver, Mitochondrial Proteins, Models, Chemical, Oxidoreductases, N-Demethylating, Rats, Sarcosine, Sarcosine Dehydrogenase, Tetrahydrofolates
Show Abstract · Added January 20, 2015
Dimethylglycine dehydrogenase (EC 1.5.99.2) and sarcosine dehydrogenase (EC 1.5.99.1) are flavoproteins which catalyze the oxidative demethylation of dimethylglycine to sarcosine and sarcosine to glycine, respectively. During these reactions tightly bound tetrahydropteroylpentaglutamate (H4PteGlu5) is converted to 5,10-methylene tetrahydropteroylpentaglutamate (5,10-CH2-H4PteGlu5), although in the absence of H4PteGlu5, formaldehyde is produced. Single turnover studies using substrate levels of the enzyme (2.3 microM) showed pseudo-first-order kinetics, with apparent first-order rate constants of 0.084 and 0.14 s-1 at 23 and 48.3 microM dimethylglycine, respectively, for dimethylglycine dehydrogenase and 0.065 s-1 at 47.3 microM sarcosine for sarcosine dehydrogenase. The rates were identical in the absence or presence of bound tetrahydropteroylglutamate (H4PteGlu). Titration of the enzymes with substrate under anaerobic conditions did not disclose the presence of an intermediate semiquinone. The effect of dimethylglycine concentration upon the rate of the dimethylglycine dehydrogenase reaction under aerobic conditions showed nonsaturable kinetics suggesting a second low-affinity site for the substrate which increases the enzymatic rate. The Km for the high-affinity active site was 0.05 mM while direct binding for the low-affinity site could not be measured. Sarcosine and dimethylthetin are poor substrates for dimethylglycine dehydrogenase and methoxyacetic acid is a competitive inhibitor at low substrate concentrations. At high dimethylglycine concentrations, increasing the concentration of methoxyacetic acid produces an initial activation and then inhibition of dimethylglycine dehydrogenase activity. When these compounds were added in varying concentrations to the enzyme in the presence of dimethylglycine, their effects upon the rate of the reaction were consistent with the presence of a second low-affinity binding site on the enzyme which enhances the reaction rate. When sarcosine is used as the substrate for sarcosine dehydrogenase the kinetics are Michaelis-Menten with a Km of 0.5 mM for sarcosine. Also, methoxyacetic acid is a competitive inhibitor of sarcosine dehydrogenase with a Ki of 0.26 mM. In the absence of folate, substrate and product determinations indicated that 1 mol of formaldehyde and of sarcosine or glycine were produced for each mole of dimethylglycine or sarcosine consumed with the concomitant reduction of 1 mol of bound FAD.
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18 MeSH Terms
Folate transport in the choroid plexus.
Chen CP, Wagner C
(1975) Life Sci 16: 1571-81
MeSH Terms: Animals, Biological Transport, Choroid Plexus, Dinitrophenols, Folic Acid, In Vitro Techniques, Kinetics, Oxygen, Phenobarbital, Phenytoin, Probenecid, Sodium, Swine, Tetrahydrofolates
Added January 20, 2015
0 Communities
1 Members
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14 MeSH Terms
Ethanol stimulates 5-methyltetrahydrofolate accumulation in isolated rat liver cells.
Horne DW, Briggs WT, Wagner C
(1978) Biochem Pharmacol 27: 2069-74
MeSH Terms: Animals, Ethanol, In Vitro Techniques, Liver, Rats, Tetrahydrofolates, Time Factors
Added January 20, 2015
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7 MeSH Terms
Transport of 5-methyltetrahydrofolic acid and folic acid in freshly isolated hepatocytes.
Horne DW, Briggs WT, Wagner C
(1978) J Biol Chem 253: 3529-35
MeSH Terms: Animals, Biological Transport, Active, Folic Acid, In Vitro Techniques, Kinetics, Liver, Male, Rats, Sodium, Tetrahydrofolates
Added January 20, 2015
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10 MeSH Terms
Enzymatic preparation of high specific activity radiolabeled (I)-L-5-methyltetrahydropteroylglutamate.
Horne DW, Briggs WT, Wagner C
(1977) Anal Biochem 83: 615-21
MeSH Terms: Chromatography, Thin Layer, Iodine Radioisotopes, Isotope Labeling, Tetrahydrofolate Dehydrogenase, Tetrahydrofolates
Added January 20, 2015
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5 MeSH Terms
Studies on the transport mechanism of 5-methyltetrahydrofolic acid in freshly isolated hepatocytes: effect of ethanol.
Horne DW, Briggs WT, Wagner C
(1979) Arch Biochem Biophys 196: 557-65
MeSH Terms: Alcohols, Anaerobiosis, Animals, Azides, Biological Transport, Ethanol, In Vitro Techniques, Kinetics, Liver, Male, Methotrexate, Pyrazoles, Rats, Structure-Activity Relationship, Tetrahydrofolates
Added January 20, 2015
0 Communities
1 Members
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15 MeSH Terms