Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

BALB/c mice were immunized with a synthetic co-factor of the aromatic amino acid hydroxylases, 6,7-dimethyl-5,6,7,8-tetrahydropterin, conjugated to albumin. Hybridoma cell lines isolated from the immunized mice secreted monoclonal antibodies reacting specifically with the pterin molecule and monoclonal antibodies which were found to bind phenylalanine hydroxylase. Several lines of evidence were consistent with the anti-phenylalanine hydroxylase antibodies being anti-idiotype antibodies mimicking the pterin molecule and binding to the pterin binding site of phenylalanine hydroxylase. (a) An anti-idiotype monoclonal antibody, NS7, when reimmunized into mice produced anti-pterin antibodies consistent with NS7 being an internal image anti-idiotypic antibody. (b) NS7 antibody was prevented from binding to phenylalanine hydroxylase when a competitive inhibitor of phenylalanine hydroxylase enzyme activity, 6,7-dimethyl-7,8-dihydropterin, was bound to phenylalanine hydroxylase. (c) NS7 antibody was shown to bind to a wide range of pterin-requiring enzymes: phenylalanine, tyrosine and tryptophan hydroxylases, dihydropteridine reductase, dihydrofolate reductase, and sepiapterin reductase. Thus the NS7 antibody has successfully mimicked a common portion of the pterin cofactors utilized by these enzymes and demonstrated structure homology in their pterin binding sites despite their diverse function and little amino acid sequence homology except among the three aromatic amino acid hydroxylases.
 ...
PMID:Structural similarities among enzyme pterin binding sites as demonstrated by a monoclonal anti-idiotypic antibody. 196 5

The natural killer-like cell line YT constitutively expresses GTP-cyclohydrolase activity whereas 6-pyruvoyltetrahydropterin synthase and sepiapterin reductase are absent. The product, dihydroneopterin triphosphate, is dephosphorylated and oxidized causing neopterin to accumulate in the cells. The activities of the H4biopterin synthesizing enzymes are not controlled by IFN-gamma or the synergistic action of both IFN-gamma and IL-2 as has been shown for monocytes/macrophages (Huber C. et al. (1984) J. Exp. Med. 160, 310) and CD4+ T cells, respectively (Ziegler I. et al. (1990) J. Biol. Chem. 265, 17026). Sepiapterin reductase specifically is induced by incubation of the cells with sepiapterin, leaving GTP-cyclohydrolase, 6-pyruvoyltetrahydropterin synthase and other enzymes related to pteridine metabolism (dihydropteridine reductase, dihydrofolate reductase) unaffected. The data indicate that H4biopterin synthesis is individually regulated in the diverse cellular components of the immune system.
 ...
PMID:Control of pteridine biosynthesis in the natural killer-like cell line YT. 203 22

The only known role for 6(R)-5,6,7,8-tetrahydrobiopterin (BH4) is as the cofactor for the aromatic amino acid hydroxylases. However, BH4 has been shown to be synthesized by cells that do not contain any hydroxylase activity, suggesting that it may have still undiscovered functions. Our finding of much higher levels of BH4 and GTP cyclohydrolase, the first enzyme of de novo BH4 biosynthesis, in rat reticulocytes compared to mature erythrocytes raised the possibility that BH4 might play a role in erythrocyte maturation. We have now demonstrated, by using murine erythroleukemia (MEL) cells as a model for erythrogenesis, that BH4 synthesis is required for proliferation of these cells. Inhibition of BH4 biosynthesis in rapidly dividing MEL cells with N-acetylserotonin, a potent inhibitor of sepiapterin reductase, the terminal enzyme in the BH4 biosynthetic pathway, results in inhibition of DNA synthesis and mitogenesis without induction of hemoglobin synthesis. The inhibition of DNA synthesis is reversed by repletion of cellular BH4 levels with sepiapterin, a pterin that is readily taken up by the cells and converted to BH4 by the sequential reductions of sepiapterin reductase and dihydrofolate reductase. Treatment of MEL cells with hexamethylene bisacetamide, an inducer of differentiation, results in a decrease in BH4 synthesis accompanied by a cessation of growth and concomitant hemoglobin synthesis. The inhibition of proliferation induced by hexamethylene bisacetamide can be reversed by maintaining high intracellular levels of BH4, which also decreases the amount of hemoglobin. The mechanism of the BH4 effect has not yet been elucidated, but it appears as though BH4 synthesis is more intimately linked with cell proliferation than with the differentiation process.
 ...
PMID:Tetrahydrobiopterin, the cofactor for aromatic amino acid hydroxylases, is synthesized by and regulates proliferation of erythroid cells. 276 2

The ability of the enzyme dihydrofolate reductase to catalyze the formation of tetrahydrobiopterin from dihydrobiopterin was used to develop a method for measuring the activity of this enzyme in vivo. This method can be used to determine the activity of the enzyme in tissues as well as the extent and duration of inhibition of the enzyme by antifolates. Sepiapterin, which is converted to dihydrobiopterin by the enzyme sepiapterin reductase, was as effective a precursor as dihydrobiopterin and has been used in these studies because of its greater stability relative to dihydrobiopterin. Assay conditions must be established for each tissue and enzyme activity can be determined either by measuring the rate of disappearance of dihydrobiopterin or the rate of formation of tetrahydrobiopterin.
 ...
PMID:In vivo measurement of dihydrofolate reductase and its inhibition by antifolates. 318 62

The enzymatic activities of GTP cyclohydrolase, sepiapterin reductase, dihydropterin reductase and dihydrofolate reductase were determined in the ocular tissues of rat, rabbit, calf and human. The enzymatic activities of the pteridine biosynthesis and the content of tetrahydropteridine (BH4) were higher in retina and ciliary body-iris as compared with lens tissue in all mammalian species tested. The activities of the pteridine synthesizing enzymes and BH4 content were decreased in human senile cataracts as compared with age-matched clear human lenses. The loss of BH4 may result in lenticular proteins more susceptible to oxidation and contribute to high molecular weight protein formation in cataracts.
 ...
PMID:The enzymatic activities of GTP cyclohydrolase, sepiapterin reductase, dihydropteridine reductase and dihydrofolate reductase; and tetrahydrobiopterin content in mammalian ocular tissues and in human senile cataracts. 388 Dec 14

The biosynthesis of tetrahydrobiopterin from either dihydroneopterin triphosphate, sepiapterin, dihydrosepiapterin or dihydrobiopterin was investigated using extracts from human liver, dihydrofolate reductase and purified sepiapterin reductase from human liver and rat erythrocytes. The incorporation of hydrogen in tetrahydrobiopterin was studied in either 2H2O or in H2O using unlabeled NAD(P)H or (R)-(4-2H)NAD(P)H or (S)-(4-2H)NAD(P)H. Dihydrofolate reductase catalyzed the transfer of the pro-R hydrogen of NAD(P)H during the reduction of 7,8-dihydrobiopterin to tetrahydrobiopterin. Sepiapterin reductase catalyzed the transfer of the pro-S hydrogen of NADPH during the reduction of sepiapterin to 7,8-dihydrobiopterin. In the presence of partially purified human liver extracts one hydrogen from the solvent is introduced at position C(6) and the 4-pro-S hydrogen from NADPH is incorporated at each of the C(1') and C(2') position of BH4. Label from the solvent is also introduced into position C(3'). These results suggest that dihydrofolate reductase is not involved in the biosynthesis of tetrahydrobiopterin from dihydroneopterin triphosphate. They are consistent with the assumption of the occurrence of a 6-pyruvoyl-tetrahydropterin intermediate, which is proposed to be formed upon triphosphate elimination from dihyroneopterin triphosphate, and via an intramolecular redox reaction. Our results suggest that the reduction of 6-pyruvoyl-tetrahydropterin might be catalyzed by sepiapterin reductase.
 ...
PMID:Tetrahydrobiopterin biosynthesis. Studies with specifically labeled (2H)NAD(P)H and 2H2O and of the enzymes involved. 388 18

The regulation of GTP-cyclohydrolase (GTP-CH) activity and tetrahydrobiopterin (BH4) levels in the adrenal cortex were studied in intact and hypophysectomized rats. Treatment with a single dose of reserpine (5 mg/kg) or insulin-induced hypoglycemia (4 h) elevated adrenocortical BH4 3-fold by 10 h; BH4 levels remained elevated after 24 h and returned to control levels by 48-72 h. GTP-CH was significantly increased 24 h after hypoglycemic shock, and the increased enzyme activity preceded the changes in BH4 levels after reserpine treatment. Two and a half hours of stress by immobilization also increased GTP-CH activity and BH4 levels in the adrenal cortex. The activities of sepiapterin reductase and dihydrofolate reductase, putative enzymes in the biosynthetic pathway from GTP to BH4, were not increased by reserpine. Both reserpine and insulin increased the apparent maximum velocity for GTP, with no increase in the affinity of the enzyme for its substrate, further suggesting that the experimental treatments induce the synthesis of GTP-CH. Hypophysectomy completely blocked the reserpine-dependent increase in both cortical GTP-CH activity and BH4 content. The administration of purified porcine ACTH to intact and hypophysectomized rats elevated adrenocortical GTP-CH activity and cofactor levels. Synthetic ACTH-(1-24) also enhanced the enzyme activity and BH4 levels in the adrenal cortex. Thus, pituitary control of adrenal cortical GTP-CH synthesis and biopterin levels appears to be mediated through the secretion of ACTH. The changes in enzyme activity and cofactor levels after activation of the hypothalamo-hypophyseal axis or ACTH administration suggest that BH4, a cofactor for certain monooxygenases, has some function, as yet unknown, in the adaptive changes of the adrenal cortex in response to stress.
 ...
PMID:Hormonal regulation of guanosine triphosphate cyclohydrolase activity and biopterin levels in the rat adrenal cortex. 613 42

1. Pteridine cofactor of phenylalanine hydroxylase (EC 1.14.16.1) and dihydropteridine reductase (EC 1.6.99.7) in the phenylalanine hydroxylating system have been studied in the fetal rat liver. 2. Activities of pteridine cofactor and dihydropteridine reductase were measured as about 6 and 50%, respectively, of the levels of adult liver in the liver from fetuses on 20 days of gestation, at this stage the activity of phenylalanine hydroxylase was almost negligible in the liver. 3. Development of the activity of sepiapterin reductase (EC 1.1.1.153), an enzyme involved in the biosynthesis of pteridine cofactor, was studied in rat liver during fetal (20-22 days of gestation), neonatal and adult stages comparing with the activity of dihydrofolate reductase (EC 1.5.1.3). Activities of the enzymes were about 80 and 50%, respectively, of the adult levels at 20 days of gestation. 4. Some characteristics of sepiapterin reductase and dihydropteridine reductase of fetal liver were reported.
 ...
PMID:Pteridine cofactor of phenylalanine hydroxylase in fetal rat liver. 640 90

1. The crab-eating monkey (Macaca fascicularis) has been studied for enzymes which react in the biosynthesis of pteridine cofactor of phenylalanine hydroxylase: 2. Rather high activity of sepiapterin reductase (EC 1.1.1.153)(0.130 mumol) and measurable activity of dihydrofolate reductase (EC 1.5.1.3)(0.039 mumol), (in amount of substrate reduced/hr/mg protein at 37 degrees C) were found in the crude extract from the liver. 3. Sepiapterin reductase was observed, in blood, only in the erythrocytes while dihydrofolate reductase was observed both in erythrocytes and leucocytes. 4. Activity of pteridine cofactor of phenylalanine hydroxylase was detected in the extract of the liver. 5. Sepiapterin reductase was partially purified from the liver, and was studied in the mol. wt, coenzyme-requirement, pH optimum, KmS and inhibitors.
 ...
PMID:Pteridine-metabolizing enzymes of Macaca fascicularis. 703 83

The murine macrophage cell line RAW 264 constitutively synthesizes tetrahydrobiopterin (BH4), the cofactor required for the hydroxylation of the aromatic amino acids and for the production of nitric oxide. Stimulation of the cells with interferon-gamma and lipopolysaccharide induced the production of nitric oxide and increased BH4 levels further. When the cells were stimulated in the presence of 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of BH4 biosynthesis, biopterin levels decreased by 90% within 6 hr, whereas nitrite production was essentially unaffected. Pretreatment of the cells for 12 hr with DAHP decreased intracellular BH4 concentrations by > 95% yet inhibited the cytokine-stimulated production of nitric oxide by only 50%. However, pretreatment with DAHP plus N-acetylserotonin, an inhibitor of sepiapterin reductase, the terminal enzyme of the BH4 biosynthetic pathway, decreased biopterin levels by > 99% and inhibited nitric oxide synthesis by 90%. This inhibition could be reversed by loading the cells with dihydrobiopterin, a precursor of BH4 via the dihydrofolate reductase salvage pathway. In addition, these studies revealed that N-acetylserotonin has a direct inhibitory effect on nitric oxide synthesis, acting in a BH4-independent manner. The results presented here support previous suggestions, based on experiments with isolated enzymes, that BH4 is absolutely required for cytokine-stimulated nitric oxide production in macrophages and they suggest that only a small fraction of the total intracellular BH4 pool in macrophages is utilized in the production of fully active nitric oxide synthase.
 ...
PMID:Tetrahydrobiopterin is required for cytokine-induced nitric oxide production in a murine macrophage cell line (RAW 264). 767 92


1 2 Next >>