Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The production and release of proline was measured in cleaned ova of Schistosoma mansoni. Proline was found to be released at approximately 76 mumoles/100 cc of ova water/hr. This high rate of proline production was found to correlate with extremely active proline synthetic enzymes in the ova. Ornithine-delta-transaminase, which converts ornithine to delta 1-pyrroline-5-carboxylic acid, was found to be twice that of adult schistosomes and over seven times that of rat liver. delta 1-pyrroline-5-carboxylic acid reductase, which converts delta 1-pyrroline-5-carboxylic acid to proline, is also more active than the adult isoenzyme and 35 times more active than the rat liver isoenzyme. These data suggest that proline emanating from the ova may play a role in stimulating fibrosis in the granulomata of schistosomiasis.
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PMID:Schistosomiasis: proline production and release by ova. 668 1

Incubation of mixed human saliva with arginine, ornithine, and proline for 30 min to 2 h at 40 degrees C leads to an appreciable consumption of the above amino acids. The rate of utilization is 0.2 to 0.5 ncat/ml of saliva. The rate of urea loss is higher by an order of magnitude: up to 11 ncat/ml. Putrescin, urea (after incubation with arginine), and ammonium are identified as the products of these reactions. The biological significance of such reactions is believed to consist in neutralization of carbohydrate fermentation products. The detected consumption of amino acids and urea indicates that mixed human saliva contains urease, arginase, ornithine decarboxylase, and, probably, proline reductase. Since the origin of these enzymes is probably bacterial, changes in their activity in the saliva can be regarded as an indicator of dysbacteriosis and a diagnostically important parameter.
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PMID:[The utilization of amino acids and urea by human oral fluid]. 947 2

The protozoan parasite, Giardia duodenalis, shares many metabolic and genetic attributes of the bacteria, including fermentative energy metabolism which relies heavily on pyrophosphate rather than adenosine triphosphate and as a result contains two typically bacterial glycolytic enzymes which are pyrophosphate dependent. Pyruvate decarboxylation and subsequent electron transport to as yet unidentified anaerobic electron acceptors relies on a eubacterial-like pyruvate:ferredoxin oxidoreductase and an archaebacterial/eubacterial-like ferredoxin. The presence of another 2-ketoacid oxidoreductase (with a preference for alpha-ketobutyrate) and multiple ferredoxins in Giardia is also a trait shared with the anaerobic bacteria. Giardia pyruvate:ferredoxin oxidoreductase is distinct from the pyruvate dehydrogenase multienzyme complex invariably found in mitochondria. This is consistent with a lack of mitochondria, citric acid cycle, oxidative phosphorylation and glutathione in Giardia. Giardia duodenalis actively consumes oxygen and yet lacks the conventional mechanisms of oxidative stress management, including superoxide dismutase, catalase, peroxidase, and glutathione cycling, which are present in most eukaryotes. In their place Giardia contains a prokaryotic H2O-producing NADH oxidase, a membrane-associated NADH peroxidase, a broad-range prokaryotic thioredoxin reductase-like disulphide reductase and the low molecular weight thiols, cysteine, thioglycolate, sulphite and coenzyme A. NADH oxidase is a major component of the electron transport pathway of Giardia which, in conjunction with disulphide reductase, protects oxygen-labile proteins such as ferredoxin and pyruvate:ferredoxin oxidoreductase against oxidative stress by maintaining a reduced intracellular environment. As the terminal oxidase, NADH oxidase provides a means of removing excess H+, thereby enabling continued pyruvate decarboxylation and the resultant production of acetate and adenosine triphosphate. A further example of the bacterial-like metabolism of Giardia is the utilisation of the amino acid arginine as an energy source. Giardia contain the arginine dihydrolase pathway, which occurs in a number of anaerobic prokaryotes, but not in other eukaryotes apart from trichomonads and Chlamydomonas reinhardtii. The pathway includes substrate level phosphorylation and is sufficiently active to make a major contribution to adenosine triphosphate production. Two enzymes of the pathway, arginine deiminase and carbamate kinase, are rare in eukaryotes and do not occur in higher animals. Arginine is transported into the trophozoite via a bacterial-like arginine:ornithine antiport. Together these metabolic pathways in Giardia provide a wide range of potential drug targets for future consideration.
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PMID:Anaerobic bacterial metabolism in the ancient eukaryote Giardia duodenalis. 950 42

Nitric oxide synthases (NOS) have a bidomain structure comprised of an N-terminal oxygenase domain and a C-terminal reductase domain. The oxygenase domain binds haem, (6R)-5,6,7,8-tetrahydro-l-biopterin (tetrahydrobiopterin) and arginine, is the site where nitric oxide synthesis takes place and contains determinants for dimeric interactions. A novel scintillation proximity assay has been established for equilibrium and kinetic measurements of substrate, inhibitor and cofactor binding to a recombinant N-terminal haem-binding domain of rat neuronal NOS (nNOS). Apparent Kd values for nNOS haem-domain-binding of arginine and Nomega-nitro-L-arginine (nitroarginine) were measured as 1.6 microM and 25 nM respectively. The kinetics of [3H]nitroarginine binding and dissociation yielded an association rate constant of 1.3x10(4) s-1.M-1 and a dissociation rate constant of 1.2x10(-4) s-1. These values are comparable to literature values obtained for full-length nNOS, suggesting that many characteristics of the arginine binding site of NOS are conserved in the haem-binding domain. Additionally, apparent Kd values were compared and were found to be similar for the inhibitors, L-NG-monomethylarginine, S-ethylisothiourea, N-iminoethyl-L-ornithine, imidazole, 7-nitroindazole and 1400W (N-[3-(aminomethyl) benzyl] acetamidine). [3H]Tetrahydrobiopterin bound to the nNOS haem domain with an apparent Kd of 20 nM. Binding was inhibited by 7-nitroindazole and stimulated by S-ethylisothiourea. The kinetics of interaction with tetrahydrobiopterin were complex, showing a triphasic binding process and a single off rate. An alternating catalytic site mechanism for NOS is proposed.
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PMID:Nitroarginine and tetrahydrobiopterin binding to the haem domain of neuronal nitric oxide synthase using a scintillation proximity assay. 957 68

Clostridium sticklandii utilizes combinations of amino acids for growth by Stickland reactions. Proline is an efficient electron acceptor in these reactions and is reduced to 5-aminovalerate. Proline can be partly synthesized from ornithine by the action of ornithine aminotransferase and delta1-pyrroline-5-carboxylate (PCA) reductase. Both enzymes were present in crude extracts of C. sticklandii in sufficient activity of 0.93 nkat (mg protein)(-1) and 4.3 nkat (mg protein)(-1), respectively, whereas enzymes involved in proline biosynthesis from glutamate were not detected. PCA reductase was purified to homogeneity in a three-step procedure involving ammonium sulfate precipitation, affinity chromatography with Procion Red and gel filtration on Sephadex GF200. The homogeneous enzyme was most likely an octamer of 230 kDa with a subunit size of 25 kDa as obtained by SDS-PAGE and 28.9 kDa as calculated from the sequence. Apparent Km values for PCA and NADH were 0.19 mM and 0.025 mM, respectively. The enzyme also catalysed in vitro the reverse reaction, the oxidation of proline, at alkaline pH values above 8 and higher substrate concentrations (apparent Km values: 1.55 mM for proline and 10.5 mM for NAD at pH 10.0). Studies with growing cells of C. sticklandii and [15N]proline revealed that proline is not oxidized in vivo because 15N was solely detected by HPLC-MS in 5-aminovalerate as the product of proline reduction. The proC gene encoding PCA reductase of C. sticklandii was cloned, sequenced and heterologously expressed in Escherichia coli. The enzyme exhibited high homologies to PCA reductases from different sources. Thus, C. sticklandii is able to synthesize the electron acceptor proline from ornithine (a degradation product of arginine) by action of ornithine aminotransferase and PCA reductase.
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PMID:Proline biosynthesis from L-ornithine in Clostridium sticklandii: purification of delta1-pyrroline-5-carboxylate reductase, and sequence and expression of the encoding gene, proC. 1022 Jan 61

Almost all iron uptake by fungi involves reduction from Fe(III) to Fe(II) in order to facilitate ligand exchange. This leads to two mechanisms: uptake before reduction, or reduction before uptake. Many fungi secrete specific hydroxamate siderophores when short of iron. The mechanism with uptake before reduction is described in the context of siderophore synthesis and usage, since it applies to many (but not all) siderophores. The hydroxamate functional group is synthesized from ornithine by N5 hydroxylation and acylation. In most fungal siderophores, two or three modified ornithines are joined together by a non-ribosomal peptide synthetase. The transcription of these genes is regulated by an iron activated repressor. There is evidence that the iron-free siderophore may be stored in intracellular vesicles until secretion is required. After loading with iron, re-entry is likely to be via a proton symport. In some fungi, siderophores are used for iron storage. The iron is liberated by an NADPH-linked reductase. The second mechanism starts with Fe(III) reduction. In yeast, this is catalysed by an NADPH-linked transmembrane reductase, which has homology with the NADPH oxidase of neutrophils. There are two closely similar reductases with overlapping roles in Fe(III) and Cu(II) reduction, while the substrates for reduction include Fe(III)-siderophores. External reductants, which may be important in certain fungi, include 3-hydroxyanthranilic acid, melanin, cellobiose dehydrogenase and 2,5-dimethylhydroquinone. In yeast, a high-affinity iron uptake pathway involves reoxidation of Fe(II) to Fe(III), probably to confer specificity for iron. This is catalysed by a copper protein which has homology with ceruloplasmin, and is closely coupled to Fe(III) transport. The transcription of these genes is regulated by an iron-inhibited activator. Because of its copper requirement, the high-affinity pathway is blocked by disruption of genes for copper metabolism. A low-affinity uptake transports Fe(II) directly and is important in anoxic growth. In many fungi, mechanisms with internal or external reduction are both important. The external reduction is applicable to almost any Fe(III) complex, while internal reduction is more efficient at low iron but requires a siderophore permease through which toxins might enter. Both mechanisms require close coupling of Fe(III) reduction and Fe(II) utilization in order to minimize production of active oxygen.
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PMID:Iron uptake by fungi: contrasted mechanisms with internal or external reduction. 1090 54

To elucidate the involvement of proteolysis in the regulation of stationary-phase adaptation, the clpA, clpX, and clpP protease mutants of Escherichia coli were subjected to proteome analysis during growth and during carbon starvation. For most of the growth-phase-regulated proteins detected on our gels, the clpA, clpX, or clpP mutant failed to mount the growth-phase regulation found in the wild type. For example, in the clpP and clpA mutant cultures, the Dps protein, the WrbA protein, and the periplasmic lysine-arginine-ornithine binding protein ArgT did not display the induction typical for late-stationary-phase wild-type cells. On the other hand, in the protease mutants, a number of proteins accumulated to a higher degree than in the wild type, especially in late stationary phase. The proteins affected in this manner include the LeuA, TrxB, GdhA, GlnA, and MetK proteins and alkyl hydroperoxide reductase (AhpC). These proteins may be directly degraded by ClpAP or ClpXP, respectively, or their expression could be modulated by a protease-dependent mechanism. From our data we conclude that the levels of most major growth-phase-regulated proteins in E. coli are at some point controlled by the activity of at least one of the ClpP, ClpA, and ClpX proteins. Cultures of the strains lacking functional ClpP or ClpX also displayed a more rapid loss of viability during extended stationary phase than the wild type. Therefore, regulation by proteolysis seems to be more important, especially in resting cells, than previously suspected.
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PMID:Global role for ClpP-containing proteases in stationary-phase adaptation of Escherichia coli. 1248 47

The biosynthesis and catabolism of lysine in Penicillium chrysogenum is of great interest because these pathways provide 2-aminoadipic acid, a precursor of the tripeptide delta-L-2-aminoadipyl-L-cysteinyl-D-valine that is an intermediate in penicillin biosynthesis. In vivo conversion of labelled L-lysine into two different intermediates was demonstrated by HPLC analysis of the intracellular amino acid pool. L-lysine is catabolized to 2-aminoadipic acid by an omega-aminotransferase and to saccharopine by a lysine-2-ketoglutarate reductase. In lysine-containing medium both activities were expressed at high levels, but the omega-aminotransferase activity, in particular, decreased sharply when ammonium was used as the nitrogen source. The omega-aminotransferase was partially purified, and found to accept L-lysine, L-ornithine and, to a lesser extent, N-acetyl-L-lysine as amino-group donors. 2-Ketoglutarate, 2-ketoadipate and, to a lesser extent, pyruvate served as amino group acceptors. This pattern suggests that this enzyme, previously designated as a lysine-6-aminotransferase, is actually an omega-aminotransferase. When 2-ketoadipate is used as substrate, the reaction product is 2-aminoadipic acid, which contributes to the pool of this intermediate available for penicillin biosynthesis. The N-terminal end of the purified 45-kDa omega-aminotransferase was sequenced and was found to be similar to the corresponding segment of the OAT1 protein of Emericella (Aspergillus) nidulans. This information was used to clone the gene encoding this enzyme.
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PMID:Lysine is catabolized to 2-aminoadipic acid in Penicillium chrysogenum by an omega-aminotransferase and to saccharopine by a lysine 2-ketoglutarate reductase. Characterization of the omega-aminotransferase. 1604 80

Glutamate 5-kinase (G5K) makes the highly unstable product glutamyl 5-phosphate (G5P) in the initial, controlling step of proline/ornithine synthesis, being feedback-inhibited by proline or ornithine, and causing, when defective, clinical hyperammonaemia. We determined two crystal structures of G5K from Escherichia coli, at 2.9 A and 2.5 A resolution, complexed with glutamate and sulphate, or with G5P, sulphate and the proline analogue 5-oxoproline. E. coli G5K presents a novel tetrameric (dimer of dimers) architecture. Each subunit contains a 257 residue AAK domain, typical of acylphosphate-forming enzymes, with characteristic alpha(3)beta(8)alpha(4) sandwich topology. This domain is responsible for catalysis and proline inhibition, and has a crater on the beta sheet C-edge that hosts the active centre and bound 5-oxoproline. Each subunit contains a 93 residue C-terminal PUA domain, typical of RNA-modifying enzymes, which presents the characteristic beta(5)beta(4) sandwich fold and three alpha helices. The AAK and PUA domains of one subunit associate non-canonically in the dimer with the same domains of the other subunit, leaving a negatively charged hole between them that hosts two Mg ions in one crystal, in line with the G5K requirement for free Mg. The tetramer, formed by two dimers interacting exclusively through their AAK domains, is flat and elongated, and has in each face, pericentrically, two exposed active centres in alternate subunits. This would permit the close apposition of two active centres of bacterial glutamate-5-phosphate reductase (the next enzyme in the proline/ornithine-synthesising route), supporting the postulated channelling of G5P. The structures clarify substrate binding and catalysis, justify the high glutamate specificity, explain the effects of known point mutations, and support the binding of proline near glutamate. Proline binding may trigger the movement of a loop that encircles glutamate, and which participates in a hydrogen bond network connecting active centres, which is possibly involved in the cooperativity for glutamate.
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PMID:A novel two-domain architecture within the amino acid kinase enzyme family revealed by the crystal structure of Escherichia coli glutamate 5-kinase. 1732 44

Proline metabolism in mammals involves two other amino acids, glutamate and ornithine, and five enzymatic activities, Delta(1)-pyrroline-5-carboxylate (P5C) reductase (P5CR), proline oxidase, P5C dehydrogenase, P5C synthase and ornithine-delta-aminotransferase (OAT). With the exception of OAT, which catalyzes a reversible reaction, the other four enzymes are unidirectional, suggesting that proline metabolism is purpose-driven, tightly regulated, and compartmentalized. In addition, this tri-amino-acid system also links with three other pivotal metabolic systems, namely the TCA cycle, urea cycle, and pentose phosphate pathway. Abnormalities in proline metabolism are relevant in several diseases: six monogenic inborn errors involving metabolism and/or transport of proline and its immediate metabolites have been described. Recent advances in the Human Genome Project, in silico database mining techniques, and research in dissecting the molecular basis of proline metabolism prompted us to utilize functional genomic approaches to analyze human genes which encode proline metabolic enzymes in the context of gene structure, regulation of gene expression, mRNA variants, protein isoforms, and single nucleotide polymorphisms.
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PMID:Functional genomics and SNP analysis of human genes encoding proline metabolic enzymes. 1850 9


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