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:2.5.1.47 (cysteine synthase)
625 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The primary metabolic defect in 5-oxoprolinuria (pyroglutamic aciduria) is the lack of glutathione synthetase. The mechanism of the concomitant overproduction of 5-oxoproline was studied using cell-free extracts of erythrocytes from control individuals and from patients with 5-oxoprolinuria. Such extracts catalyzed the synthesis of 5-oxoproline from L-glutamate. Addition of ATP, Mg ions and alpha-aminobutyrate was needed for optimal activity. The conversion of glutamate to 5-oxoproline occurred in two steps, catalyzed by gamma-glutamyl-cysteine synthetase and gamma-glutamyl cyclotransferase, respectively. Extracts of erythrocytes from control subjects and patients with 5-oxoprolinuria had identical capacity to synthesize 5-oxoproline. The conversion of glutamate to 5-oxoproline was markedly inhibited by reduced glutathione, which exerted its effect on the gamma-glutamyl-cysteine synthetase step. The following mechanism is postulated for the overproduction of 5-oxoproline in 5-oxoprolinuria: the deficiency of glutathione synthetase causes a lack of glutathione which is an essential feed-back inhibitor in the initial step of its biosynthesis. Therefore gamma-glutamyl-cysteine is produced in excessive amounts and it is subsequently converted to 5-oxoproline (and cysteine) by gamma-glutamyl cyclotransferase. This overproduction of 5-oxoproline exceeds the capacity of the 5-oxoprolinase and 5-oxoproline accumulates in body fluids.
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PMID:On the mechanism of 5-oxoproline overproduction in 5-oxoprolinuria. 126 Oct 42

Glutathione-depleted hepatocytes, by incubation with diethylmaleate (DEM) or phorone (2,6-dimethyl-2,5-heptadiene-4-one), i.e., substrates of the GSH S-transferases (EC 2.5.1.18), showed rates of gluconeogenesis from various precursors significantly lower than controls; however the rate of glucose synthesis from fructose was similar to that of controls. Isolated hepatocytes from rats pretreated with those substrates 1 h before isolation to deplete hepatic glutathione (GSH) also showed a decrease of the rate of gluconeogenesis from lactate plus pyruvate. Incubation of hepatocytes with L-buthionine sulfoximine, a specific inhibitor of gamma-glutamyl-cysteine synthetase (EC 6.3.2.2), resulted in a decreased rate of gluconeogenesis from lactate plus pyruvate only when GSH values were lower than 1 mumol/g cells. Freeze-clamped livers from GSH-depleted rats showed a higher concentration of malate and glycerol 3-phosphate, indicating that GSH depletion probably affects phosphoenolpyruvate carboxykinase and glycerol-3-phosphate dehydrogenase activities. Several indicators of cell viability, such as lactate dehydrogenase leakage, malondialdehyde accumulation, ATP concentration, or urea synthesis from different precursors, were not affected by GSH depletion under the experimental conditions used here. Besides, the GSH/GSSG ratio remained unchanged in all cases.
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PMID:Effects of glutathione depletion on gluconeogenesis in isolated hepatocytes. 402 24

Mn(II) has been proposed as a potential modulator of various important CNS enzymes, particularly glutamine synthetase, which is compartmentalized in the cytoplasm of glia. Previous studies demonstrated that total glial Mn(II) was 50-75 microM, of which 30-40% occurs in the cytoplasm. In the present study, electron spin resonance (ESR) was used to determine that the concentration of free cytoplasmic Mn(II) in cultured chick glial cells is 0.8 (+/- 0.2) microM, very near Kd for the GS-Mn(II) complex. No free Mn(II) could be detected in glial mitochondria. Association of Mn(II) with brain glutamine synthetase (GS) was assessed under in vivo conditions in the presence of millimolar Mg(II) by trapping bound 54Mn(II) ions in the active site with irreversible inhibitors, namely methionine-sulfoximine (MSOX) or specific analogues thereof plus ATP. Ovine brain tissue was lysed directly into buffer containing Mn(II), 3 mM Mg(II), 1 mM MSOX, 1 mM ATP, 200 mM KCl, and 20 mM NaCl. Alternatively, primary cultures of chick glial cells were permeabilized into these inactivation mixtures. alpha-Methyl-D,L-prothionine-S,R-sulfoximine was used to specifically inhibit the mechanistically-related enzyme gamma-glutamyl-cysteine synthetase prior to specific inactivation of GS by alpha-ethyl-D,L-methionine-S,R-sulfoximine. Even in the presence of 2-3 mM Mg(II), with only 5-10 microM Mn(II) present, approximately 20-30% of GS subunits were trapped with bound Mn(II). These results indicate that brain GS exhibits a high degree of specificity for binding Mn(II) over Mg(II) and that Mn(II) binds to GS to a significant extent under in vivo conditions.
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PMID:Kinetic, ESR, and trapping evidence for in vivo binding of Mn(II) to glutamine synthetase in brain cells. 791 Mar 78

A fluorimetric technique previously described for other tissues has been applied to determine levels of glutathione and its synthetic rates in ocular tissues of Hartley guinea-pigs. Monochlorobimane forms a stable, fluorescent adduct with glutathione in a reaction catalyzed by glutathione-S-transferase. The fluorescent signal recorded over time is directly proportional to the synthetic rate of glutathione. Lens, cornea and retina were homogenized and cytosolic fractions dialyzed overnight to deplete endogeneous glutathione. Glutathione synthetic rates were determined from a mixture of glutathione precursors and co-factors, viz. cysteine+dithiothreitol, glutamate+glycine, ATP and Mg++ in the presence of monochlorobimane. The mixture was supplemented with glutathione-S-transferase to catalyze the formation of the fluorescent adduct. Glutathione synthetic rates were determined in the absence and presence of buthionine sulfoximine, an inhibitor of gamma-glutamyl cysteine synthetase. The difference in fluorescence change over time in the presence and absence of buthionine sulfoximine was used to estimate glutathione synthesis. Basal levels of glutathione in pre-dialyzed cytosolic fractions of the lens, cornea, and retina were 21.8 +/- 2.2, 36.5 +/- 4.1 and 38.6 +/- 2.8 nmol mg-1 protein, respectively. The maximal glutathione synthetic rates in these tissues were 0.52 +/- 0.04, 2.25 +/- 0.67 and 3.35 +/- 0.65 nmol min-1 mg-1 protein, respectively. When gamma-glutamyl cysteine is used as a precursor instead of cysteine, the glutathione synthetase activities from lenses and retinas were 0.19 +/- 0.08 and 1.54 +/- 0.76 nmol-1 min mg-1 protein.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:A simple technique to determine glutathione (GSH) levels and synthesis in ocular tissues as GSH-bimane adduct: application to normal and galactosemic guinea-pigs. 843 34

Glucose-dependent energy required for glioma metabolism depends on hexokinase, which is mainly bound to mitochondria. A decrease in intracellular pH leads to a release of hexokinase-binding, which in turn decreases glucose phosphorylation, ATP content, and cell proliferation. Thus, intracellular pH might be a target for therapy of gliomas, and a search for agents able to modulate intracellular pH was initiated. Hypericin, a natural photosensitizer, displays numerous biological activities when exposed to light. Its mechanism and site of action at the cellular level remain unclear, but it probably acts by a type II oxygen-dependent photosensitization mechanism producing singlet oxygen. Hypericin is also able to induce a photogenerated intracellular pH drop, which could constitute an alternative mechanism of hypericin action. In human glioma cells treated for 1 h with 2.5 microg/ml hypericin, light exposure induced a fall in intracellular pH. In these conditions, mitochondria-bound hexokinase was inhibited in a light- and dose-dependent manner, associated with a decreased ATP content, a decrease of mitochondrial transmembrane potential, and a depletion of intracellular glutathione. Hexokinase protein was effectively released from mitochondria, as measured by an ELISA using a specific anti-hexokinase antibody. In addition to decreased glutathione, a response to oxidative stress was confirmed by the concomitant increase in mRNA expression of gamma-glutamyl cysteine synthetase, which catalyzes the rate-limiting step in overall glutathione biosynthesis, and is subject to feedback regulation by glutathione. Hypericin also induced a dose- and light-dependent inhibition of [3H]thymidine uptake and induced apoptosis, as demonstrated by annexin V-FITC binding and cell morphology. This study confirmed the mitochondria as a primary target of photodynamic action. The multifaceted action of hypericin involves the alteration of mitochondria-bound hexokinase, initiating a cascade of events that converge to alter the energy metabolism of glioma cells and their survival. In view of the complex mechanism of action of hypericin, further exploration is warranted in a perspective of its clinical application as a potential phototoxic agent in the treatment of glioma tumors.
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PMID:Light-induced photoactivation of hypericin affects the energy metabolism of human glioma cells by inhibiting hexokinase bound to mitochondria. 986 36

Experiments were conducted to investigate the effect of S nutrition and availability on the forms of S and N in the endosperm cavity and endosperm of wheat, and on the capacity of the endosperm to utilize those compounds for the synthesis of proteins. Plants were grown in solution culture with 2 mM N and either 200 microM S (high-S) or 50 microM S (low-S) and all nutrients were withdrawn at various times from booting until 8 d post-anthesis. Sulphate was the major form of soluble S in the endosperm cavity and endosperm of high-S plants during the time of rapid grain development. By contrast, glutathione (GSH) was the major form of soluble S in the endosperm cavity and in the endosperm in low-S plants. Crude extracts of endosperm tissue from both high-S and low-S plants supported (i) the hydrolysis of GSH to gamma-glutamyl cysteine and glycine, and of gamma-glutamyl cysteine to glutamate and cysteine, and (ii) sulphate-dependent PPi-ATP exchange and the sulphydration of O-acetylserine catalysed by ATP sulphurylase and cysteine synthase, respectively. High-S nutrition enhanced the in vitro rates of ATP sulphurylase and cysteine synthase.
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PMID:Sulphur nutrition affects delivery and metabolism of S in developing endosperms of wheat. 1145 12

Understanding the mechanisms of free energy transfer in metabolism is fundamental to understanding how the chemical forces that sustain the molecular organization of the cell are distributed. Recent studies of molecular motors (1-3) and ATP-driven proton transport (4-6) describe how chemical potential is transferred at the molecular level. These systems catalyze energy transfer through structural change and appear to be dedicated exclusively to their coupling tasks (7, 8). Here we report the discovery of a new class of energy-transfer system. It is a biosynthetic pump composed of cysteine biosynthesis enzymes, ATP sulfurylase and O-acetylserine sulfhydrylase, each with its own catalytic function and from whose interactions emerge new function: the hydrolysis of ATP. The hydrolysis is kinetically and energetically linked to the chemistry catalyzed by ATP sulfurylase, the first enzyme in the cysteine biosynthetic pathway, in such a way that each molecule of ATP hydrolyzed, each stroke of the pump, produces 1 equivalent of that enzyme's product. These findings integrate cysteine metabolism and broaden our understanding of the ways in which higher order allostery is used to effect free energy transfer.
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PMID:Cysteine biosynthetic enzymes are the pieces of a metabolic energy pump. 1208

The identification, isolation and characterization of a new Aspergillus nidulans positive-acting gene metR, which encodes a transcriptional activator of sulphur metabolism, is reported. metR mutants are tight auxotrophs requiring methionine or homocysteine for growth. Mutations in the metR gene are epistatic to mutations in the negative-acting sulphur regulatory scon genes. The metR coding sequence is interrupted by a single intron of 492 bp which is unusually long for fungi. Aspergillus nidulans METR is a member of bZIP family of DNA-binding proteins. The bZIP domains of METR and the Neurospora crassa CYS3 transcriptional activator of sulphur genes are highly similar. Although Neurospora cys-3 gene does not substitute for the metR function, a chimeric metR gene with a cys-3 bZIP domain is able to transform the DeltametR mutant to methionine prototrophy. This indicates that METR recognizes the same regulatory sequence as CYS3. The metR gene is not essential, as deletion mutants are viable and have similar phenotype as point mutants. In contrast to the Neurospora cys-3, transcription of the metR gene was found to be regulated neither by METR protein nor by sulphur source. Transcription of metR gene is derepressed in the sconB2 mutant. Transcription of genes encoding sulphate permease, homocysteine synthase, cysteine synthase, ATP-sulphurylase, and sulphur controller--sconB is strongly regulated by the metR gene product and depends on the character of the metR mutation and sulphur supplementation.
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PMID:The Aspergillus nidulans metR gene encodes a bZIP protein which activates transcription of sulphur metabolism genes. 1289 30

In this study, the phosphoproteome of Corynebacterium glutamicum, an industrially important soil bacterium of the Corynebacterium/Mycobacterium/Nocardia (CMN) group of Gram-positive bacteria, was investigated by two different detection methods: first, by in vivo radio-labeling using [(33)P]-phosphoric acid with subsequent autoradiography and second, by immunostaining with phosphoamino acid-specific monoclonal antibodies. After two-dimensional gel electrophoresis (2-DE), around 60 [(33)P]-labeled protein spots were visualized and around 90 antibody-decorated protein spots detected; 31 of the protein spots were detected with both methods. By peptide mass fingerprinting, 41 different proteins were identified, namely 5-enolpyruvylshikimate 3-phosphate synthase, aconitase, acyl-CoA carboxylase, acyl-CoA synthetase, ATP (synthase alpha- and beta-chain), carbamoyl-phosphate synthase, citrate synthase, cysteine synthase, DnaK, the elongation factors G, P, Ts and Tu, enolase, fructose bisphosphate aldolase, fumarase, Gap dehydrogenase, glutamine synthetase I, glycine hydroxymethyltransferase, GroEL2, GTPase, heat-inducible transcriptional repressor DnaJ2, inorganic pyrophosphatase, isocitrate dehydrogenase, ketol-acid reductoisomerase, lactate dehydrogenase, leucine-tRNA ligase, lipoamide dehydrogenase, methionine synthase, O-acetylhomoserine sulfhydrylase, pyruvate carboxylase, pyruvate kinase, pyruvate oxidase, ribosomal protein S1, RNA polymerase (beta-subunit), succinyl-CoA:CoA transferase, transketolase and UDP-N-acetylmuramoyl-L-alanine ligase, besides a hypothetical 35k protein and a hypothetical glucose kinase. Both detection techniques were used to create a phosphoproteome map. Additionally, the influence of nitrogen deprivation on the phosphoproteome of C. glutamicum was investigated.
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PMID:Towards a phosphoproteome map of Corynebacterium glutamicum. 1292 88

We examined the role of GSH in survival and cell death using GCS-2 cells that are deficient in glutamate cysteine ligase (gamma-glutamyl cysteine synthetase, gammaGCS), an enzyme essential for GSH synthesis. Cells maintained in 2.5 mM GSH have GSH levels that are approximately 2% of wild type and grow indefinitely; however, they express both pro- and anti-apoptotic Bcl-2 family members and have detectable levels of cytoplasmic cytochrome C. Withdrawal of GSH from the medium results in a fall in intracellular GSH to undetectable levels, decreased mitochondrial dehydrogenase activity, decreased anti-apoptotic factor RNAs, increased pro-apoptotic factor RNAs, additional cytochrome C release, and a fall in ATP levels; however, cells continue to grow for another 24h. At 48 h, these trends continue with the exception that mitochondrial membrane potential and ATP levels rise; DNA fragmentation begins at 48 h. Thus, severe reduction of GSH to 2% of wild type produces a metastable state compatible with survival, but complete absence of GSH triggers apoptosis.
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PMID:Survival and cell death in cells constitutively unable to synthesize glutathione. 1623 16


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