Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.17.1.4 (xanthine dehydrogenase)
1,236 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In Arabidopsis thaliana, urease transcript levels increased sharply between 2 and 4 d after germination (DAG) and were maintained at maximal levels until at least 8 DAG. Seed urease specific activity declined upon germination but began to increase in seedlings 2 DAG, reaching approximately 75% of seed activity by 8 DAG. Urea levels showed a small transient increase 1 DAG and then approximately paralleled urease activity, reaching maximal levels at approximately 9 DAG. Urease inhibition with phenylphosphorodiamidate resulted in a 2- to 4-fold increase in urea levels throughout seedling development. Arginine pools (0-8 DAG) changed approximately in parallel with the urea pool. Consistent with arginine being a major source of urea, arginase activity increased 10-fold in the interval 0 to 6 DAG. Allopurinol, a xanthine dehydrogenase inhibitor, had no effect on urea levels up to 3 DAG but reduced the urea pool by 30 to 40% during the interval 5 to 8 DAG, suggesting that purine degradation contributed to the urea pool well after germination, if at all. in aged Arabidopsis seeds, there was correlation between phenylphosphorodiamidate inactivation of urease and germination inhibition, the latter overcome by NH4NO3 or amino acids. Since urease activity, urea precursor, and urea increase in young seedlings, and since urease inactivation results in a nitrogen-reversible inhibition of germination, we propose that urease recycles urea-nitrogen in the seedling.
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PMID:Essential role of urease in germination of nitrogen-limited Arabidopsis thaliana seeds. 777 May 20

Serratia marcecens 2CC-1 utilizes quinaldic acid (quinoline 2-carboxylic acid) as sole source of carbon, nitrogen and energy. Growth of strain 2CC-1 on quinaldic acid as well as on nicotinic acid and hypoxanthine was inhibited completely by the molybdate antagonist tungstate, whereas growth on kynurenic acid and 6-hydroxynicotinic acid was not affected by tungstate. The synthesis of the molybdenum-containing hydroxylases quinaldic acid 4-oxidoreductase and nicotinic acid 6-oxidoreductase was found to be inducible. In addition, Serratia marcescens 2CC-1 produced a constitutively expressed xanthine oxidoreductase. Quinaldic acid 4-oxidoreductase was purified 1075-fold with a recovery of 5%. For catalytic activity, artificial electron acceptors were necessary. The 95-100-kDa enzyme was a heterodimer with subunit molecular masses of 75-80 kDa and 18-19 kDa. Quinaldic acid 4-oxidoreductase contained 2.3-3.7 g atom of iron and 0.5-0.6 g atom of molybdenum per mol of enzyme. The absorption spectrum exhibited maxima at 280 nm, 334 nm, 480 nm and a shoulder at 550 nm, with A280/A334 = 4.8, A280/A450 = 10.0, A280/A480 = 9.4, and A450/A550 = 1.6, suggesting the absence of a flavin cofactor. Acridine, quinacrine, ethylenediaminetetraacetate, 2,2'-dipyridyl, 1,10-phenanthroline and iodoacetate did not affect enzyme activity. p-Hydroxymercuribenzoate, m-arsenite, cyanide and methanol were effective inhibitors of quinaldic acid 4-oxidoreductase. Cyanide-inhibited enzyme was reactivated by treatment with S2-, indicating the presence of a pterin molybdenum cofactor with a monooxo-monosulfidotype molybdenum center. Quinaldic acid 4-oxidoreductase showed a very high substrate specificity, quinaldic acid being the only substrate found to be transformed significantly.
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PMID:Microbial metabolism of quinoline and related compounds. XVIII. Purification and some properties of the molybdenum- and iron-containing quinaldic acid 4-oxidoreductase from Serratia marcescens 2CC-1. 835 32

Xanthine dehydrogenase (XDH) is induced in Comamonas acidovorans cells incubated in a limited medium with hypoxanthine as the only carbon and nitrogen source. The enzyme has been purified to homogeneity using standard techniques and characterized. It contains two subunits with M(r) values of 90 and 60 kDa. Gel filtration studies show the enzyme to have an alpha 2 beta 2 native structure. No precursor form of the enzyme is observed on Western blot analysis of cell extracts obtained at various stages of enzyme induction. Metal analysis of the purified enzyme shows 1.1 Mo, 4.0 Fe, and 3.6 phosphorus atoms per alpha beta protomer. Cofactor analysis shows the enzyme to contain a single molybdopterin mononucleotide and one FAD per alpha beta protomer. Electron spin resonance and circular dichroism spectral studies of the oxidized and reduced forms of the enzyme suggest the Fe centers to be two nonidentical [2Fe-2S] clusters. Electron spin resonance signals due to Mo(V) and neutral FAD radical are also observed in the reduced form of the enzyme. Purified enzyme preparations ranged from 70% to 100% functionality. The enzyme is irreversibly inactivated by CN- and is inhibited on incubation with allopurinol. With xanthine and NAD+ as substrates the enzyme has a specific activity of 50 units/mg, a kcat value of 120 s-1, an activity/flavin ratio of 1930, and respective Km values of 66 and 160 mM. Using 8-D-xanthine as substrate, a DV value of 1.8 is found with no change in Km. Thus, the Km and KD values of the enzyme for xanthine are equal. These data show Comamonas XDH to exhibit structural properties similar to bovine milk xanthine oxidase/dehydrogenase and to chicken liver xanthine dehydrogenase. Although the bacterial enzyme exhibits a 6-7-fold greater turnover rate than bovine or avian enzymes, the catalytic efficiencies (as measured by V/K) are similar for all three enzymes.
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PMID:Purification and characterization of a prokaryotic xanthine dehydrogenase from Comamonas acidovorans. 861 34

Aldehyde oxidase and xanthine dehydrogenase are a group of ubiquitous hydroxylases, containing a molybdenum cofactor (MoCo) and two iron-sulfur groups. Plant aldehyde oxidase and xanthine dehydrogenase activities are involved in nitrogen metabolism and hormone biosynthesis, and their corresponding genes have not yet been isolated. Here we describe a new gene from tomato, which shows the characteristics of a MoCo containing hydroxylase. It shares sequence homology with xanthine dehydrogenases and aldehyde oxidases from various organisms, and similarly contains binding sites for two iron-sulfur centers and a molybdenum-binding region. However, it does not contain the xanthine dehydrogenase conserved sequences thought to be involved in NAD binding and in substrate specificity, and is likely to encode an aldehyde oxidase-type activity. This gene was designated tomato aldehyde oxidase 1 (TAO1). TAO1 belongs to a multigene family, whose members are shown to map to clusters on chromosomes 1 and 11. MoCo hydroxylase activity is shown to be recognized by antibodies raised against recombinant TAO1 polypeptides. Immunoblots reveal that TAO1 cross-reacting material is ubiquitously expressed in various organisms, and in plants it is mostly abundant in fruits and rapidly dividing tissues.
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PMID:TAO1, a representative of the molybdenum cofactor containing hydroxylases from tomato. 899 97

The xpt and pbuX genes from Bacillus subtilis were cloned, and their nucleotide sequences were determined. The xpt gene encodes a specific xanthine phosphoribosyltransferase, and the pbuX gene encodes a xanthine-specific purine permease. The genes have overlapping coding regions, and Northern (RNA) blot analysis indicated an operon organization. The translation of the second gene, pbuX, was strongly dependent on the translation of the first gene, xpt. Expression of the operon was repressed by purines, and the effector molecules appear to be hypoxanthine and guanine. When hypoxanthine and guanine were added together, a 160-fold repression was observed. The regulation of expression was at the level of transcription, and we propose that a transcription termination-antitermination control mechanism similar to the one suggested for the regulation of the purine biosynthesis operon exists. The expression of the xpt-pbuX operon was reduced when hypoxanthine served as the sole nitrogen source. Under these conditions, the level of the hypoxanthine- and xanthine-degrading enzyme, xanthine dehydrogenase, was induced more than 80-fold. The xanthine dehydrogenase level was completely derepressed in a glnA (glutamine synthetase) genetic background. Although the regulation of the expression of the xpt-pbuX operon was found to be affected by the nitrogen source, it was normal in a glnA mutant strain. This result suggests the existence of different signalling pathways for repression of the transcription of the xpt-pbuX operon and the induction of xanthine dehydrogenase.
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PMID:Xanthine metabolism in Bacillus subtilis: characterization of the xpt-pbuX operon and evidence for purine- and nitrogen-controlled expression of genes involved in xanthine salvage and catabolism. 909 51

Fourteen Rhodobacter capsulatus mutants unable to grow with xanthine as sole nitrogen source were isolated by random Tn5 mutagenesis. Five of these Tn5 insertions were mapped within two adjacent chromosomal EcoRI fragments hybridizing to oligonucleotides synthesized according to conserved amino acid sequences of eukaryotic xanthine dehydrogenases. DNA sequence analysis of this region revealed two open reading frames, designated xdhA and xdhB, encoding xanthine dehydrogenase. The deduced amino acid sequence of XDHA contains binding sites for two [2Fe-2S] clusters and FAD, whereas XDHB is predicted to contain the molybdopterin cofactor. In contrast to R. capsulatus, these three cofactor binding sites reside within a single polypeptide chain in eukaryotic xanthine dehydrogenases. The amino acid sequence of xanthine dehydrogenase from R. capsulatus showed a higher degree of similarity to eukaryotic xanthine dehydrogenases than to the xanthine dehydrogenase-related aldehyde oxidoreductase from Desulphovibrio gigas. The expression of an xdhA-lacZ fusion was induced when hypoxanthine or xanthine was added as sole nitrogen source. Mutations in nifR1 (ntrC) and nifR4 (rpoN, encoding sigma54) had no influence on xdh gene expression. A putative activator sensing the availability of substrate seems to respond to xanthine but not to hypoxanthine. The transcriptional start site of xdhA was mapped by primer extension analysis. Comparison with known promoter elements revealed no significant homology. Xanthine dehydrogenase from R. capsulatus was purified to homogeneity. The enzyme consists of two subunits with molecular masses of 85 kDa and 50 kDa respectively. N-terminal amino acid sequencing of both subunits confirmed the predicted start codons. The molecular mass of the native enzyme was determined to be 275 kDa, indicating an alpha2beta2-subunit structure. Analysis of the molybdenum cofactor of xanthine dehydrogenase from R. capsulatus revealed that it contains the molybdopterin cofactor and not a molybdopterin dinucleotide derivative.
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PMID:Xanthine dehydrogenase from the phototrophic purple bacterium Rhodobacter capsulatus is more similar to its eukaryotic counterparts than to prokaryotic molybdenum enzymes. 951 10

In humans, adenine phosphoribosyltransferase (APRT, EC 2.4.2.7) deficiency can manifest as nephrolithiasis, interstitial nephritis, and chronic renal failure. APRT catalyzes synthesis of AMP from adenine and 5-phosphoribosyl-1-pyrophosphate. In the absence of APRT, 2,8-dihydroxyadenine (DHA) is produced from adenine by xanthine dehydrogenase (XDH) and can precipitate in the renal interstitium, resulting in kidney disease. Treatment with allopurinol controls formation of DHA stones by inhibiting XDH activity. Kidney disease in APRT-deficient mice resembles that seen in humans. By age 12 wk, APRT-deficient male mice are, on average, mildly anemic and smaller than normal males. They have extensive renal interstitial damage (assessed by image analysis) and elevated blood urea nitrogen (BUN), and their creatinine clearance rates, which measure excretion of infused creatinine as an estimate of glomerular filtration rate (GFR), are about half that of wild-type males. APRT-deficient males treated with allopurinol in the drinking water had normal BUN and less extensive visible renal damage, but creatinine clearance remained low. Throughout their lifespans, homozygous null female mice manifested significantly less renal damage than homozygous null males of the same age. APRT-deficient females showed no significant impairment of GFR at age 12 wk. Consequences of APRT deficiency in male mice are more pronounced than in females, possibly due to differences in rates of adenine or DHA synthesis or to sex-determined responses of the kidneys.
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PMID:Chronic renal failure in a mouse model of human adenine phosphoribosyltransferase deficiency. 968 17

Molybdenum-containing enzymes of the hydroxylase class (such as xanthine dehydrogenase, aldehyde oxidase and nicotinate dehydrogenase) require a terminal sulphur atom attached to the molybdenum to hydroxylate their specific substrates. The transulphurylation reaction is carried out in Drosophila melanogaster by the product of the ma-I gene. In Aspergillus nidulans, the activity of the isofunctional and homologous HxB protein is needed in at least two different metabolic contexts, when the organism grows on purines and when it grows on nicotinate as nitrogen sources. We show here that the expression of the hxB gene is not constitutive. It is induced independently and additively by the inducers of the purine and of the nicotinate utilization pathways. Each of these induction pathways is affected independently by mutations in their cognate genes, uric acid induction by mutations in the UaY protein and nicotinate and 6-nicotinate induction by those in the hxnR/aplA complex. It is, in both metabolic contexts, exquisitely sensitive to nitrogen metabolite repression and highly dependent on the AreA GATA factor.
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PMID:The hxB gene, necessary for the post-translational activation of purine hydroxylases in Aspergillus nidulans, is independently controlled by the purine utilization and the nicotinate utilization transcriptional activating systems. 1009 75

During the screening for Rhodobacter capsulatus mutants defective in xanthine degradation, one Tn5 mutant which was able to grow with xanthine as a sole nitrogen source only in the presence of high molybdate concentrations (1 mM), a phenotype resembling Escherichia coli mogA mutants, was identified. Unexpectedly, the corresponding Tn5 insertion was located within the moeA gene. Partial DNA sequence analysis and interposon mutagenesis of regions flanking R. capsulatus moeA revealed that no further genes essential for molybdopterin biosynthesis are located in the vicinity of moeA and revealed that moeA forms a monocistronic transcriptional unit in R. capsulatus. Amino acid sequence alignments of R. capsulatus MoeA (414 amino acids [aa]) with E. coli MogA (195 aa) showed that MoeA contains an internal domain homologous to MogA, suggesting similar functions of these proteins in the biosynthesis of the molybdenum cofactor. Interposon mutants defective in moeA did not exhibit dimethyl sulfoxide reductase or nitrate reductase activity, which both require the molybdopterin guanine dinucleotide (MGD) cofactor, even after addition of 1 mM molybdate to the medium. In contrast, the activity of xanthine dehydrogenase, which binds the molybdopterin (MPT) cofactor, was restored to wild-type levels after the addition of 1 mM molybdate to the growth medium. Analysis of fluorescent derivatives of the molybdenum cofactor of purified xanthine dehydrogenase isolated from moeA and modA mutant strains, respectively, revealed that MPT is inserted into the enzyme only after molybdenum chelation, and both metal chelation and Mo-MPT insertion can occur only under high molybdate concentrations in the absence of MoeA. These data support a model for the biosynthesis of the molybdenum cofactor in which the biosynthesis of MPT and MGD are split at a stage when the molybdenum atom is added to MPT.
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PMID:Activity of the molybdopterin-containing xanthine dehydrogenase of Rhodobacter capsulatus can be restored by high molybdenum concentrations in a moeA mutant defective in molybdenum cofactor biosynthesis. 1049 4

The distribution of the Mo-enzymes aldehyde oxidase (AO; EC 1.2.3.1) xanthine dehydrogenase (XDH; EC 1.2.1.37) and nitrate reductase (NAD(P)H NR; EC 1.6.6.1-2) was studied along the longitudinal and transversal axes of maize (Zea mays L. cv. Jubily) nodal roots as affected by nitrogen sources and salinity. Activities of the Mo-enzymes were considerably enhanced under mild saline conditions. The activities of AO and XDH increased following addition of ammonium to the nutrient solution. Immunoblot analysis with antibodies raised against maize AO protein revealed increased levels of AO proteins in root tips of ammonium fed plants. Application of salinity to nitrate fed plants did not affect the enzyme protein level, although it enhanced the activity of the Mo-hydroxylases. The specific activities of the Mo-enzymes were the highest in root tips (0-1 cm segments) while on the transversal axis maximal activity was observed in the stele or vascular cylinder. Activity staining of AO after native PAGE of root extracts revealed four bands of AO proteins (AO1-4) capable of oxidizing a number of aliphatic and aromatic aldehydes. Increased AO activity in maize nodal roots grown with ammonium, and salinity were observed mainly at the AO3 and AO4 bands. Tips and stele contained primarily AO3 and AO4, and only traces of AO1 and AO2. SDS-PAGE of root extracts followed by Western blots revealed, besides the major 150 kD subunit of AO, two polypeptides with molecular masses of 72 and 85 kD located specifically in the cortex. Part of the polymorphism of AO in plant roots may be related to the allocation of distinct isoforms to different regions of the root, although the specific metabolic roles of the different bands have not been established.
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PMID:Distribution of the Mo-enzymes aldehyde oxidase, xanthine dehydrogenase and nitrate reductase in maize (Zea mays L.) nodal roots as affected by nitrogen and salinity. 1077 39


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