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At least 19 recordsLinked to original sources
PubMedDate not supplied

Kinetic studies of cytoplasmic and mitochondrial aconitate hydratases from rat liver.

The kinetic properties of the cytoplasmic and mitochondrial aconitate hydratases of rat liver have been studied by measuring the formation of the two products from each of the three tricarboxylic acids used as substrate. The kinetic properties of the two enzymes are very similar; the similarity of the Km values for each of the three substrates is particularly remarkable. The results are discussed with particular reference to a possible role of the cytoplasmic aconitate hydratase in the process of gluconeogenesis. With both aconitate hydratases, substrate activation by citrate and D-isocitrate has been observed.

Aconitate Hydratase↗
PubMed1976

Regulation of aconitate hydratase activity from rat kidney cortex by bicarbonate.

1. The increase in pH value and bicarbonate concentration stimulated citrate synthesis from pyruvate and malate, inhibiting simultaneously conversion of isocitrate to citrate. 2. Bicarbonate inhibited competitively the activity of aconitate hydratase, probably binding with the two active sites of the enzyme. The Ki values for the cytoplasmic and mitochondrial enzyme were, respectively, 27 and 38 mM. The pH optimum for both forms of the enzyme in Tris-HCl buffer was in the range 7.8-8.6, and in bicarbonate buffer varied from 7.2 to 8.0, depending on the form of the enzyme and the substrate used. 3. Only free, completely dissociated citrate anion acts as a substrate for aconitate hydratase. 4. The role of aconitate hydratase as a factor controlling the rate of citrate metabolism in kidney in metabolic alkalosis is discussed.

Aconitate Hydratase↗
PubMedDate not supplied

Developmental changes of rat liver cytoplasmic and mitochondrial aconitate hydratases.

The developmental patterns of the activity of cytoplasmic and mitochondrial aconitate hydratses of rat liver have been studied. Both activities are low in foetal liver, with respect to adult levels, and begin to increase after birth. The activity of the mitochondrial enzyme reaches a maximum about two days after birth, then decreasing gradually to adult level. The activity of the cytoplasmic enzyme reaches its maximum level, nearly equal to adult level, about ten days after birth. The developmental pattern of the activity of the cytoplasmic aconitate hydratase may suggest a possible role of this enzyme in gluconeogenesis.

Aconitate Hydratase↗
PubMed1979

Metabolism and defluorination of fluoroacetate in the brush-tailed possum (Trichosurus vulpecula).

The brush-tailed possum (T. vulpecula) from Western Australia was found to be nearly 150 times more resistant to fluoroacetate intoxication in vivo than the same species from South Australia. Acetone powder preparations from the liver of animals from both populations showed similar abilities to convert fluoroacetate into fluorocitrate. Aconitate hydratase activity in liver preparations from both Western Australian and South Australian animals was similarly and competitively inhibited by fluorocitrate. Both animals were capable of defluorinating fluoroacetate at similar rates by a glutathione-dependent enzymic mechanism resulting in the formation of free fluoride ion and S-carboxymethylcysteine. Glutathione was also capable of partial protection against the toxic effects of fluoroacetate in vitro by a further unelucidated mechanism.

Aconitate Hydratase↗
PubMed1975

Effect of nitrate reduction on the enzyme levels in carbon metabolism in Escherichia coli.

The activities of twelve enzymes were measured in crude extracts from cells of Escherichia coli K-10 grown aerobically or anaerobically in a defined medium in the presence or absence of nitrate. The activities of isocitrate dehydrogenase, aconitate hydratase, 2-oxoglutarate dehydrogenase, malate dehydrogenase, malic enzyme, and D-lactate dehydrogenase (NAD+-independent) were found to be higher in cells grown in nitrate respiration than in those in fermentation, but lower than in those in respiration. This finding may explain the incomplete oxidation in nitrate respiration and, on the other hand, suggests the operation of the tricarboxylic acid even under these conditions. The activities of succinate dehydrogenase and alcohol dehydrogenase in relation to the formation of fermentation product were as high in cells grown in fermentation as in those in respiration and were low in those in nitrate respiration. However, that ratio of the activities in the latter case to the activities in respiration was the same as the ratio for most enzymes in the tricarboxylic acid cycle. The level of lactate dehydrogenase (NAD+-dependent) was not affected by nitrate respiration but its activity in the extract was inhibited by nitrate and nitrite. The absence of lactate in the anaerobic culture with nitrate may be due to this inhibition as well as NADH oxidation by nitrate. Levels of glucose-6-phosphate dehydrogenase and glutamate dehydrogenase were not altered by the growth conditions and that of pyruvate dehydrogenase was low only in cells grown in fermentation.

Aconitate Hydratase↗
PubMed1977

Structural basis for aconitase activity inactivation by butanedione and binding of substrates and inhibitors.

Aconitase (citrate(isocitrate)hydro-lyase, EC 4.2.1.3) prior to activation demonstrates a single binding site for substrates and inhibitors. On the basis of kinetic experiments, at pH 8.5 and 37 degrees C, with monomeric butanedione in borate, this binding site was found to contain a single arginine residue. Dissociation constants at pH 8.5 and 37 degrees C, determined from inhibitory effects on butanedione inactivation rates are: citrate, 0.74 mM; D-isocitrate, 0.33 mM: cis-aconitate, 0.52 mM; tricarballytate, 0.42 mM; trans-aconitate, 0.025 mM. Corresponding dissociation constants for the active enzyme are: tricarballylate, 0.39 mM; trans-aconitate, 0.14 mM. Active site Fe2+ added to the enzyme on activation is therefore not required for binding. Km values are: citrate, 0.23 mM and cis-aconitate 0.012 mM. Binding to active enzyme is considered to be transition state binding.

Aconitate Hydratase↗
PubMed2026

Clinical and Genetic Spectrum of ACO2-Linked Dominant Optic Atrophy.

IMPORTANCE: Aconitase 2 (ACO2) gene variants are one of the most frequent causes of dominant optic atrophy (DOA). However, the associated phenotypes and genotypes still lack proper characterization. OBJECTIVE: To characterize the clinical and genetic spectrum of ACO2-related DOA and evaluate genotype-phenotype correlations. DESIGN, SETTING, AND PARTICIPANTS: This was a retrospective case series to describe the ophthalmological examination of novel DOA cases with a heterozygous ACO2 variant. Data were collected from 13 reference centers in ophthalmology from France and Great Britain between January 2021 and September 2025. Included participants were those patients with OA and confirmed heterozygous or compound heterozygous ACO2 variants. EXPOSURES: DOA cases with a heterozygous ACO2 variant. MAIN OUTCOMES AND MEASURES: Positive molecular diagnosis for ACO2 variants by next-generation sequencing, clinical examination including age at diagnosis, sex, best-corrected visual acuity (BCVA), retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL) thickness, visual field mean deviation (MD), and fundus examination. RESULTS: Data for 55 patients (median [IQR] age at diagnosis for 45 patients, 24 [8-51] years; 33 male [67%]) from 37 families with ACO2 variants were compiled. Analyses were conducted on 49 patients who were strictly heterozygous or compound heterozygous with the c.220C>G benign variant. Clinical data disclosed a high variability of severity, from pauci-symptomatic up to legal blindness. Median BCVA was 0.46 logMAR (Snellen equivalent, 20/63; IQR 0.00-0.89; n = 45). Four patients exhibited retinal abnormalities: 3 displayed a foveopathy, and 1 had retinitis pigmentosa. There were 12 previously unreported variants (to the authors' knowledge), including the deletion of ACO2 exon 9. No correlation between BCVA and sex, age at diagnosis (Spearman ρ = -0.19; 95% CI, -0.45 to 0.07), or variant type (Kruskal-Wallis test P =.33) was found, but there was a correlation between BCVA and RNFL (Spearman ρ = -0.74; 95% CI, -0.85 to -0.54), GCL (Spearman ρ = -0.60; 95% CI, -0.79 to -0.30), and MD (Spearman ρ = -0.65; 95% CI, -0.89 to -0.31). RNFL correlated with GCL (Spearman ρ = 0.69; 95% CI, 0.42-0.87) and MD (Spearman ρ = 0.57; 95% CI, 0.14-0.85); age at diagnosis correlated with GCL (Spearman ρ = -0.37; 95% CI, -0.63 to -0.03). CONCLUSIONS AND RELEVANCE: Results of this case series reveal the high clinical heterogeneity among patients with ACO2-related DOA and demonstrated that some of these patients can also exhibit retinal abnormalities. In addition, there was a deletion of an entire ACO2 exon, emphasizing the potential importance of searching for large genomic rearrangements in patients without a molecular diagnosis. These findings support further studies to explain clinical variability, as no genotype-phenotype correlation was encountered.

Humans↗
PubMed1978

Pyruvate and citrate metabolism in the muscle tissue of Ascaris lumbricoides.

Aconitase and NAD linked isocitrate dehydrogenase were present in Ascaris lumbricoides muscle at only very low activities, whilst there were significant levels of citrate synthase, NADP linked isocitrate dehydrogenase, 2-oxoglutarate dehydrogenase and succinic thiokinase. Pyruvate dehydrogenase was present in A. lumbricoides muscle at levels comparable with mammalian tissues and results suggest that it is modulated via a phosphotransferase/phosphatase system. The tricarboxylic acid cycle intermediates, citrate, isocitrate and 2-oxoglutarate were all detected in freeze clamped muscle, but their steady state levels were considerably lower than those found in mammalian tissues.

Aconitate Hydratase↗
PubMed1978

Aconitase (E.C. 4.2.1.3) mitochondrial locus mapped to human chromosome 22: studies with Chinese hamster--human somatic cell hybrids.

Three separate somatic cell fusions were made between Chinese hamster lines and human lymphocytes containing (1) a 3/4 translocation, (2) an X/9 translocation, and (3) a 17/9 translocation. Eleven independently derived hybrids showed that only human chromosome 22 was consistently present when human ACONM was expressed and absent when human ACONM was not expressed. These studies assign a gene for human ACONM to chromosome 22, and are consistent with prior gene-mapping results.

Aconitate Hydratase↗
PubMed1979

Human lysosomal genes: arylsulfatase A and beta-galactosidase.

The segregation of human lysosomal arylsulfatase A (ARS-A) has been evaluated in 50 primary hybrid clones derived from four separate fusions involving WBCs from two unrelated individuals and three hamster cell lines. ARS-A was expressed in the hybrids as a dimeric molecule of very similar or identical subunits. The expression of this enzyme was concordant with that of mitochondrial aconitase (ACON-M), an isozyme assigned to chromosome 22, in all 50 clones and with chromosome 22 segregation in all but one of the 29 karyotyped hybrids. No other human chromosome cosegregated with 22 in these clones, suggesting that this enzyme is specified in hybrid cells by a locus (or loci) on a single chromosome. beta-Galactosidase (B-GAL) expression was analyzed with two different electrophoresis systems and with a number of cell extract preparation methods in 39 of the primary hybrid clones. The B-GAL isozyme expressed in these hybrid cells was concordant with the expression of glutathione peroxidase-1 (GPX-1), an isozyme assigned to chromosome 3, in all 39 clones and with the segregation of this chromosome in 97% of the 29 karyotyped hybrids. These observations substantiate the prior tentative assignments of an ARS-A locus to chromosome 22 and a B-GAL locus to chromosome 3 (Bruns et al., 1978a, b). The implications of the chromosome assignments of loci for 12 human lysosomal enzymes for the cellular assembly of these organelles are discussed.

Aconitate Hydratase↗
PubMed1975

Effect of boseimycin on some enzyme systems of Bacillus subtilis.

The effect of boseimycin on the in vitro activity and in vivo synthesis of alkaline phosphatase, aconitase and lactate, isocitrate, glutamate and alanine dehydrogenases was studied in Bacillus subtilis. At a subinhibitory concentration, synthesis of glutamate dehydrogenase was stimulated but alkaline phosphatase, lactate dehydrogenase and aconitase synthesis was inhibited. On the contrary, boseimycin inhibited slightly the activity of lactate dehydrogenase in cell-free extracts. Glutamate dehydrogenase and aconitase activities were not affected.

Aconitate Hydratase↗