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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The enzyme 6-phosphogluconate dehydratase has been isolated in a stable form by a simple one-step procedure using dye ligand chromatography. The role of metal ions in the activity and stability of the enzyme was investigated. As with aconitase and several other dehydratase enzymes, the active site includes an Fe4S4 cluster. In addition, the purified enzyme has been shown to contain one manganese ion per subunit, which is also essential for activity. Rapid inactivation by superoxide radical was observed, which could only partly be protected by manganous ions The purified enzyme could be stabilised by alpha-glycerophosphate in place of manganese; glycerophosphate mimics the carbon atoms 4 to 6 of the natural substrate. This suggests that the manganous ion may involved in binding this part of the substrate.
Biochem Mol Biol Int 1996 Apr
PMID:6-phosphogluconate dehydratase from Zymomonas mobilis: an iron-sulfur-manganese enzyme. 872 8

This paper presents data about the subcellular distribution of aconitases in rat liver and some properties of the aconitase activity in cytosol, mitochondria and soluble mitochondrial protein (SMP). The cytosolic and mitochondrial aconitase activity was 64.8% or 61.0% and 20.1% or 19.4% of the total rat liver aconitase activity when cis-aconitate or isocitrate was used as substrate. Aconitase activity of stored SMP and mitochondria with phosphate buffer (pH 7.4) and 0.25 M sucrose (pH 7.4) as isolation medium respectively, was reduced to an equal extent upon exposure to air. Fresh SMP preparations immediately and three hr after isolation had the same aconitase activity. It is concluded that phosphate has no role in the oxidative degradation of mitochondrial aconitase and does not inhibit it. Complete restoration of the decreased mitochondrial aconitase activity to the initial level was achieved with thiomalate and Fe2+ under anaerobic conditions or 60-70% was restored during the long period (60 min) of incubation with exogenous substrate. The aconitase activity of cytosol and mitochondria increased upon exposure to air for 7 1/2 hr. This finding is interpreted to suggest the existence of putative aconitase activity.
Comp Biochem Physiol B Biochem Mol Biol 1996 Jan
PMID:Aconitase activity in rat liver. 893 45

In this chapter, we have focused on the biochemistry of IRP-1 and the features which distinguish it from the related RNA-binding protein, IRP-2. IRP-1 is the cytoplasmic isoform of the enzyme aconitase, and, depending on iron status, may switch between enzymatic and RNA-binding activities. IRP-1 and IRP-2 are trans-acting regulators of mRNAs involved in iron uptake, storage and utilisation. The finding of an IRE in the citric acid cycle enzymes, mitochondrial aconitase and succinate dehydrogenase, suggests that the IRPs may also influence cellular energy production. These two proteins appear to bind RNAs with different but overlapping specificity, suggesting that they may regulate the stability or translation of as yet undefined mRNA targets, possibly extending their regulatory function beyond that of iron homeostasis. The interaction between the IRPs and the IRE represents one of the best characterised model systems for posttranscriptional gene control, and given that each IRP can also recognise its own unique set of RNAs, the search for new in vivo mRNA targets is expected to provide yet more surprises and insights into the fate of cytoplasmic mRNAs.
Prog Mol Subcell Biol 1997
PMID:Interaction between iron-regulatory proteins and their RNA target sequences, iron-responsive elements. 899 63

Inactivation of aconitase by oxidative stress was analyzed under the in vivo and in situ conditions of yeast cells. Treatment of yeast cells with paraquat caused a specific inactivation of aconitase without affecting the activity of other citric acid cycle enzymes. Addition of copper plus ascorbic acid to permeabilized yeast cells also inactivated aconitase, but did not affect other TCA cycle-related enzymes. Inactivation of aconitase was suggested to be due to the superoxide and hydroxyl radicals produced from the reaction of O2 with paraquat and by Fenton reaction with copper and ascorbic acid under the in vivo and in situ conditions of yeast, respectively. Citrate the substrate of aconitase effectively protected aconitase from the oxidative inactivation. Toxicity of oxygen to yeast cells can be explained by the specific inactivation of aconitase by oxygen radicals. Increased concentrations of citrate can act as a defense mechanism against oxidative inactivation of aconitase under the exposure of aerobically grown yeast to oxidative stress.
Biochem Mol Biol Int 1997 Mar
PMID:Inactivation of aconitase in yeast exposed to oxidative stress. 909 Apr 55

In filamentous fungi, lysine is synthesized via the alpha-aminoadipate pathway. In order to gain insight into this fungus-specific pathway (to date, no genes for enzymes of this pathway in filamentous fungi have been cloned) the lysine auxotrophic mutant LysF88 of Aspergillus nidulans was studied. HPLC and 1H-NMR analyses revealed that LysF88 accumulated homocitric acid in the culture supernatant. In addition, both the LysF88 mutant strain and LysF deletion strain (LysFKO) described here showed hardly any homoaconitase activity, indicating that lysF encodes homoaconitase. The lysF gene was cloned by complementation of the LysF88 mutant and sequenced. It has a size of 2397 bp, including a single intron of 72 bp. The two exons encode an open reading frame (ORF) of 2325 bp. The calculated M(r) of the homoaconitase protein (775 amino acids) is 83,943. A major and a minor transcript begin at positions -28 and -32, respectively. The 3' end of the lysF cDNA showed a poly(A) tail commencing at position +2647 following a 250 bp untranslated region after the lysF stop codon. A putative polyadenylation signal sequence (TATAAA) is located 49 bp upstream of the polyadenylation site. Computer analysis revealed 55% amino acid sequence identity between the products of the putative homoaconitase ORF of A. nidulans and that of the recently sequenced homologous Saccharomyces cerevisiae. The similarity was particularly obvious in a region of cysteine residues, which are characteristic of an iron-sulfur cluster, implying that homoaconitase contains such a cluster. The homoaconitases of A. nidulans and S. cerevisiae share only 20% sequence identity with S. cerevisiae aconitase. The pH optimum for the activity of A. nidulans homoaconitase in 0.1 M potassium phosphate buffer is between pH 8.1 and pH 8.6. Homoaconitase exhibited an apparent K(m) of 1.1 mM toward homoisocitric acid. The specific activity of homoaconitase was reduced by up to six-fold in mycelia grown in the presence of L-lysine, suggesting that it is regulated by lysine.
Mol Gen Genet 1997 Jul
PMID:The Aspergillus nidulans lysF gene encodes homoaconitase, an enzyme involved in the fungus-specific lysine biosynthesis pathway. 926 14

Administration to rats of 1,3-difluoro-2-propanol (100 mg kg-1 body weight), the major ingredient of the pesticide gliftor, resulted in accumulation of citrate in the kidney after a 3 hour lag phase. 1,3-Difluoro-2-propanol was found to be metabolized to 1,3-difluoroacetone and ultimately to the aconitate hydratase inhibitor (-) erythrofluorocitrate and free fluoride. The conversion of 1,3-difluoro-2-propanol to 1,3-difluoroacetone was found to be catalyzed by an NAD(+)-dependent alcohol dehydrogenase, while the defluorination was attributed to microsomal monooxygenase activity induced by phenobarbitone and inhibited by piperonyl butoxide. 4-Methylpyrazole was found to inhibit both of these processes in vitro and when administered (90 mg kg-1 body weight) to rats, 2 hours prior to 1,3-difluoro-2-propanol, eliminated signs of poisoning, prevented (-) erythrofluorocitrate synthesis, and markedly decreased citrate and fluoride accumulation in vivo. 4-Methylpyrazole also appeared to diminish (-) erythrofluorocitrate synthesis from fluoroacetate in vivo, and this was attributed to its capacity to inhibit malate dehydrogenase activity. The antidotal potential of 4-methylpyrazole and the potential for 1,3-difluoro-2-propanol to replace fluoroacetate (compound 1080) as a vertebrate pesticide is discussed.
J Biochem Mol Toxicol 1998
PMID:The biochemical toxicology of 1,3-difluoro-2-propanol, the major ingredient of the pesticide gliftor: the potential of 4-methylpyrazole as an antidote. 941 86

The binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with the aryl hydrocarbon (AH) receptor and subsequent changes in gene expression have been studied intensively, but the mechanisms by which these lead to toxicity are unclear. We investigated the influence of iron, previously implicated in TCDD-induced hepatic porphyria, in mice with alleles of Ahr that encode receptors with varied affinity for TCDD. The administration of iron to Ahrb-1 C57BL/6J (AH-responsive) mice before a single dose of TCDD (75 micrograms/kg) markedly potentiated not only the hepatic porphyria but also general hepatocellular damage and elevation of plasma hepatic enzymes. The formation of hydroxylated and peroxylated derivatives of uroporphyrins formed from uroporphyrinogen and the induction of a mu-glutathione transferase (GST) were consistent with the operation of an oxidative mechanism. In a comparison of C57BL/6J mice with Ahrb-2 BALB/c (AH-responsive) and Ahrd SWR and DBA/2 (AH-nonresponsive) mice, iron overcame the weak hepatic porphyria and toxicity responses in BALB/c and SWR strains but not in DBA/2. CYP1A isoforms are strongly implicated in the mechanism of porphyria, but activities were lowered by 20-30% with iron treatment, and a comparison of levels between strains did not fully account for the resistance of DBA/2 mice. Studies with the use of gel shift assays and cytosolic aconitase of the capacity of the iron regulatory protein controlling the translation of some iron metabolism proteins showed a significant difference between C57BL/6J and DBA/2 mice after the administration of TCDD. We conclude that iron potentiates both the hepatic porphyria and toxicity of TCDD in susceptible mice in an oxidative process with disturbance of iron regulatory protein capacity. Iron even overcomes the AH-nonresponsive Ahrd allele in the SWR strain but not in DBA/2 mice, which remain resistant.
Mol Pharmacol 1998 Jan
PMID:Interaction between iron metabolism and 2,3,7,8-tetrachlorodibenzo-p-dioxin in mice with variants of the Ahr gene: a hepatic oxidative mechanism. 944 32

Fungi have evolved a unique alpha-amino-adipate pathway for lysine biosynthesis. The fungal-specific enzyme homoaconitate hydratase from this pathway is moderately similar to the aconitase-family proteins from a diverse array of taxonomic groups, which have varying modes of obtaining lysine. We have used the similarity of homoaconitate hydratase to isopropylmalate isomerase (serving in leucine biosynthesis), aconitase (from the tricarboxylic acid cycle), and iron-responsive element binding proteins (cytosolic aconitase) from fungi and other eukaryotes, eubacteria, and archaea to evaluate possible evolutionary scenarios for the origin of this pathway. Refined sequence alignments show that aconitase active site residues are highly conserved in each of the enzymes, and intervening sequence sites are quite dissimilar. This pattern suggests strong purifying selection has acted to preserve the aconitase active site residues for a common catalytic mechanism; numerous other substitutions occur due to adaptive evolution or simply lack of functional constraint. We hypothesize that the similarities are the remnants of an ancestral gene duplication, which may not have occurred within the fungal lineage. Maximum likelihood, neighbor joining, and maximum parsimony phylogenetic comparisons show that the alpha-aminoadipate pathway enzyme is an outgroup to all aconitase family proteins for which sequence is currently available.
J Mol Evol 1998 Apr
PMID:A unique fungal lysine biosynthesis enzyme shares a common ancestor with tricarboxylic acid cycle and leucine biosynthetic enzymes found in diverse organisms. 954 34

Xanthomonas campestris pv campestris (Xcc) is a plant pathogenic bacterium that controls the production of pathogenicity factors in part by a cluster of genes designated rpf (regulation of pathogenicity factors). Sequence analysis of one of these genes (rpfA) revealed an open reading frame with amino acid sequence similarity to aconitases from other bacteria. Aconitase activity was lower in cellular extracts of an rpfA::Tn5 mutant than in those from the wild type. A zymogram of aconitase activity after native gel electrophoresis showed the presence of two distinct aconitases in Xcc; the major aconitase was absent in the rpfA::Tn5 mutant. This mutant also had reduced levels of extracellular enzymes and extracellular polysaccharide (EPS). Supplying rpfA in trans to the rpfA::Tn5 mutant restored both the major aconitase activity and the synthesis of these pathogenicity factors. The transcription of the genes for two extracellular enzymes (prtA, encoding a serine protease, and engXCA, encoding endoglucanase) was reduced in the rpfA mutant background. Because some eukaryotic aconitases are also involved in iron regulation, we explored a possible connection between rpfA and iron metabolism. Intracellular iron levels in the mutants were lower than in the wild type as assessed by sensitivity to the iron-activated antibiotic, streptonigrin. Wild-type bacteria grown in iron-deficient conditions had a similar sensitivity to streptonigrin as the aconitase mutant. Overall, these results suggest that a prokaryotic aconitase can also act as a regulator of gene expression and that the regulation is possibly related to changes in intracellular iron levels.
Mol Microbiol 1998 Jun
PMID:The rpfA gene of Xanthomonas campestris pathovar campestris, which is involved in the regulation of pathogenicity factor production, encodes an aconitase. 966 82

The anaerobic chytrid Piromyces sp. E2 lacks mitochondria, but contains hydrogen-producing organelles, the hydrogenosomes. We are interested in how the adaptation to anaerobiosis influenced enzyme compartmentalization in this organism. Random sequencing of a cDNA library from Piromyces sp. E2 resulted in the isolation of cDNAs encoding malate dehydrogenase, aconitase and acetohydroxyacid reductoisomerase. Phylogenetic analysis of the deduced amino acid sequences revealed that they are closely related to their mitochondrial homologues from aerobic eukaryotes. However, the deduced sequences lack N-terminal extensions, which function as mitochondrial leader sequences in the corresponding mitochondrial enzymes from aerobic eukaryotes. Subcellular fractionation and enzyme assays confirmed that the corresponding enzymes are located in the cytosol. As anaerobic chytrids evolved from aerobic, mitochondria-bearing ancestors, we suggest that, in the course of the adaptation from an aerobic to an anaerobic lifestyle, mitochondrial enzymes were retargeted to the cytosol with the concomitant loss of their N-terminal leader sequences.
Mol Microbiol 1998 Dec
PMID:Cytosolic enzymes with a mitochondrial ancestry from the anaerobic chytrid Piromyces sp. E2. 998 78


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