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:1.8.1.4 (diaphorase)
2,754 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Twenty-eight spontaneous auxotrophic aroP mutants with deletions in the azi--nadC--aroP--aceE--aceF--lpd region of the Escherichia coli K12 chromosome were characterized genetically with respect to various azi, nadC, ace and lpd markers by P1-mediated transduction. One mutant (Kdelta18; aroP--lpddelta) had a deletion which extended through the aceE and aceF genes to end within the lpd gene. The polarity of the ace operon (aceE to aceF) was confirmed. It was concluded that 10 out of 15 deletions generating a strict requirement for acetate terminated in the aceE gene. Of the ten, three mutants (Kdelta22, Cdelta41 and Cdelta41) synthesized detectable dihydrolipoamide acetyltransferase (the aceF gene product) and seven were assumed to possess deletions generating polar effects on aceF gene expression. Five deletions appeared to extend into the aceF gene. A further five deletions, which limited the expression of the ace operon without generating an Ace- phenotype or a complete Ace- phenotype, ended closest to the aroP-proximal aceE markers. The opposite ends of all these deletions appeared to terminate before (10), within (2) or extend beyond (9) the nadC gene. There was no obvious correlation between the deletion end-points and the corresponding lipoamide dehydrogenase activities, which ranged from 30 to 95% of parental levels in different deletion strains. The remaining seven deletions simply extended between the aroP and nadC genes (nad--aroPdelta) without affecting expression of the ace operon. Regulation of the synthesis of the pyruvate and alpha-ketoglutarate dehydrogenase complexes was investigated in some of the parental and deletion strains under different physiological conditions including thiamin-deprivation. The results indicate that the syntheses of the two dehydrogenase complexes are independently regulated. Expression of the lpd gene appears to be coupled to complex synthesis but can be dissociated under some conditions. Mechanisms for regulating lpd gene expression are discussed and an autogenous mechanism involving uncomplexed lipoamide dehydrogenase functioning as a negatively acting repressor at the operator site of an independent lpd gene is proposed as the simplest mechanism which is consistent with all available information.
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PMID:Biochemical genetics of the alpha-keto acid dehydrogenase complexes of Escherichia coli K12: genetic characterization and regulatory properties of deletion mutants. 34 14

Lipoic acid (lip) and 2-oxoglutarate dehydrogenase (sucA) mutants of Escherichia coli K12 exhibit a requirement for exogenous succinate during aerobic growth on glucose minimal medium. Reversion studies have shown that this requirement can be suppressed by gal-linked mutations which inactivate succinate dehydrogenase. Biochemical and genetic studies confirmed that the succinate dehydrogenase gene (sdh) is affected and that suppression is mediated by the same intergenic and indirect mechanism that generates succinate independence in partial revertants of lipoamide dehydrogenase mutants (Creaghan & Guest, 1977). A series of isogenic strains containing all combinations of mutations affecting 2-oxoglutarate dehydrogenase (sucA), succinate dehydrogenase (sdh), isocitrate lyase (aceA) and fumarate reductase (frd) in a background lacking succinate semialdehyde dehydrogenase, was constructed to assess the importance of these enzymes as sources of endogenous succinate (succinyl-CoA) during aerobic and anaerobic growth on glucose. Only strains combining a deficiency in 2-oxoglutarate dehydrogenase with the presence of an active succinate dehydrogenase required succinate for aerobic growth. In all mutants, including the triple mutant (frd sucA aceA), the succinate requirement was suppressed by inactivating succinate dehydrogenase. The aerobic growth rates of succinate-independent strains were most affected by lack of isocitrate lyase but only two mutants (sdh sucA aceA and frd sdh sucA aceA) grew faster with added succinate: the growth yields were lowered by deficiencies in isocitrate lyase and also succinate dehydrogenase. It is concluded that very little succinate is needed for biosynthesis during aerobic growth on glucose and the requirement for relatively high concentrations of succinate (2 mM) by mutants lacking 2-oxoglutarate dehydrogenase or related functions stems from the presence of active succinate dehydrogenase. Anaerobically, either isocitrate lyase or fumarate reductase is essential for succinate-independent growth on glucose.
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PMID:Succinate dehydrogenase-dependent nutritional requirement for succinate in mutants of Escherichia coli K12. 36 70

The pyruvate dehydrogenase multienzyme complex was isolated from Escherichia coli grown in the presence of [35S]sulphate. The three component enzymes were separated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and the molar ratios of the three polypeptide chains were determined by measurement of the radioactivity in each band. The chain ratio of lipoamide dehydrogenase to lipoate acetyltransferase approached unity, but there was a molar excess of chains of the pyruvate decarboxylase component. The 35S-labelled complex was also used in a new determination of the total lipoic acid content. It was found that each polypeptide chain of the lipoate acetyltransferase component appears to bear at least three lipoyl groups.
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PMID:Polypeptide-chain stoicheiometry and lipoic acid content of the pyruvate dehydrogenase complex of Escherichia coli. 37 15

Thioredoxin from Escherichia coli was shown to catalyze the reduction of insulin disulfides by dithiothreitol. A quantitative assay was developed which measures the rate of insulin reduction spectrophotometrically at 650 nm as turbidity formation from the precipitation of the free insulin B chain. Thioredoxin, at 5 microM concentration, accelerated the reaction between 0.130 mM insulin and 1.0 mM dithiothreitol at pH 7 around 20-fold. The pH optimum of the reaction was 7.5. Thioredoxins from E. coli and calf liver showed similar specific activities. Stopped flow fluorescence measurements of the rate of reduction of thioredoxin-S2 by dithiothreitol showed a second order rate constant of 1647 M-1 s-1 at pH 7.2. This is between 10(2) to 10(3) times larger than the reaction between insulin or linear model disulfides and dithiothreitol. It is consistent with a ping-pong mechanism of thioredoxin catalysis since reduced thioredoxin is known to react very fast with insulin. Thioredoxin also catalyzed lipoamide-dependent reduction of the insulin disulfides in a coupled system with NADH, lipoamide, and lipoamide dehydrogenase. The fast spontaneous reaction between dihydrolipoamide and thioredoxin-S2 provides a mechanism for NADH or pyruvate-dependent disulfide reduction. The implication of the dithiol-disulfide oxidoreductase activity of thioredoxin for the regulation of enzyme activities by thiol oxidation-reduction control is discussed.
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PMID:Thioredoxin catalyzes the reduction of insulin disulfides by dithiothreitol and dihydrolipoamide. 38 88

The molar ratio of the component enzymes of the pyruvate dehydrogenase multienzyme complex from Escherichia coli was found to be 1.8:1.7:1[pyruvate decarboxylase (E1):dihydrolipoyl transacetylase (E2):dihydrolipoyl dehydrogenase (E3)]. This ratio was determined by measuring the Coomassie blue staining of the constituent enzymes after sodium dodecyl sulfate/polyacrylamide slab gel electrophoresis. The above ratio is the average of four separate experiments with two different enzyme preparations. The average molecular weights of the individual enzymes were found to be 96,000, 76,000, and 55,000 for E1, E2, and E3, respectively, by sodium dodecyl sulfate and sodium dodecyl sulfate/8 M urea polyacrylamide gel electrophoresis and by column chromatography in 6 M guanidine . HCl. The molecular weight of E2 was reduced to 33,000-36,000 after extensive reduction and alkylation with iodoacetamide. The molecular weights of the complex, E1, and E3 were found to be 4,800,000, 182,000, and 104,000, respectively, with low-angle laser light scattering. Both E1 and E3 are dimeric under the conditions employed. If octahedral symmetry is assumed for the E2 core, a polypeptide chain ratio of 24:24:12 (E1:E2:E3) is in good agreement with the measured molar ratio of component enzymes and the molecular weight of the pyruvate dehydrogenase complex.
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PMID:Subunit stoichiometry and molecular weight of the pyruvate dehydrogenase multienzyme complex from Escherichia coli. 38 35

Limited tryptic digestion of the pyruvate dehydrogenase complex of Escherichia coli or its dihydrolipoyl transacetylase core cleaves the trypsin-sensitive transacetylase subunits into two large fragments, A (lipoyl domain) and D (subunit binding domain). Release of fragments A from the complex does not significantly affect its sedimentation coefficient or its appearance in the electron microscope. Fragment A contains the lipoyl moieties ((3)H-labeled), is acidic with an apparent isoelectric point of about 4.0, has a M(r) of 31,600 as determined by sedimentation equilibrium analysis, and has a swollen or extended structure (f/f(o) = 1.78). Fragment A exhibits anomalous properties, probably due to its acidic nature. It is resistant to staining with Coomassie blue and it migrates on sodium dodecyl sulfate/polyacrylamide gels as if it had a M(r) of 46,000-48,000. Further tryptic digestion converts fragment A into a lipoyl-containing fragment of M(r) 20,000 (fragment B) and eventually into an apparently stable product of estimated M(r) about 10,000 (fragment C). Fragment D has a compact structure of M(r) about 29,600 as determined by sedimentation equilibrium analysis in 6 M guanidinium chloride, and it possesses the intersubunit binding sites of the transacetylase, the binding sites for pyruvate dehydrogenase and dihydrolipoyl dehydrogenase, and the catalytic site for transacetylation. The assemblage of fragments D is responsible for the cube-like appearance of the transacetylase in the electron microscope. High-resolution electron micrographs of the transacetylase show fiber-like extensions, apparently corresponding to tryptic fragment A, surrounding the cube-like core.
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PMID:Subunit structure of dihydrolipoyl transacetylase component of pyruvate dehydrogenase complex from Escherichia coli. 38 41

Cell-free extracts of a streptomycin-bleached strain of Euglena gracilis var. bacillaris have been examined for enzyme systems primarily responsible for the oxidation of reduced pyridine nucelotides. NADH lipoyl dehydrogenase, NADH and NADPH oxidase, NADH and NADPH diaphorase, and NADH and NADPH cytochrome c reductase have been demonstrated. The NADPH-linked enzymes had lower activity rates and were less sensitive to N-ethyl maleimide and p-hydroxymercuribenzoate than their NADH-linked counterparts. NADH cytochrome c reductase was the most sensitive to antimycin A. Michaelis-Menten constants (Km) determined were as follows: NADH diaphorase, 350 muM; NADPH oxidase 150 muM ; NADH lipoyl dehydrogenase, 0.35 muM. Enzyme activities after storage at -5 C indicate that the diaphorases are less labile than the other tested enzymes, and the differential activities of the NADH and NADPH linked enzymes suggest that functionally they may have different roles.
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PMID:Reduced pyridine nucleotide oxidases of Eugena gracilis var. bacillaris. 40 56

The enzymatic defects in a number of Bacillus subtilis mutants of the alpha-ketoglutarate dehydrogenase complex lacking activity have been investigated. Mutants in the citK locus, as well as a series of deletions of unknown length covering the citK locus, are deficient in E1 of the complex, alpha-ketoglutarate dehydrogenase, but have normal activities of E2, dehydrolipoyl transsuccinylase, and E3, lipoamide dehydrogenase. The citK mutants and the citL22 mutant show in vitro complementation of alpha-ketoglutarate dehydrogenase complex activity. The citL22 mutant is severely deficient in lipoamide dehydrogenase activity, and, as a result, lacks activity for both the alpha-ketoglutarate and the pyruvate dehydrogenase complexes. Thus, the E3 components of both complexes are identical. The citL22 mutation maps between ura and metC on the chromosome.
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PMID:Genetics of the alpha-ketoglutarate dehydrogenase complex of Bacillus subtilis. 41 34

Mammalian pyruvate dehydrogenase multienzyme complex is inactivated when treated with a leupeptin-sensitive enzyme (termed 'inactivase') obtained from rat liver lysosomes. However, the inactivation of the overall reaction does not affect any of the component activities of the enzyme complex. By several methods it is demonstrated that treatment with the inactivase provokes the disassembly of the complex into its constituent enzyme components which, though being enzymatically active when assayed separately, are unable to catalyze the coordinated reaction sequence of pyruvate oxidation. The dissociation occurs as a consequence of limited proteolysis of the lipoate acetyltransferase core of the multienzyme complex. Isolated nicked acetyltransferase retains its complete enzymatic activity and behaves as a high-molecular-weight aggregate. The lipoamide dehydrogenase and pyruvate dehydrogenase components, however, are not cleaved by the inactivase.
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PMID:Inactivation and disassembly of the pyruvate dehydrogenase multienzyme complex from bovine kidney by limited proteolysis with an enzyme from rat liver. 44 83

The mitochondrial matrix subfractions from rat liver, kidney cortex, brain, heart, and skeletal muscle were isolated and their protein components were resolved by two-dimensional polyacrylamide gel electrophoresis, revealing between 120 and 150 components for each matrix subfraction. Excellent resolution was obtained utilizing a pH 5 to 8 gradient in the first dimension and in 8 to 13% exponential acrylamide gradient in the second dimension, increasing the number of mitochondrial matrix proteins observed 3-fold over one-dimensional systems. Protein components tentatively identified by co-migration with pure enzymes and by known tissue distributions are carbamoyl-phosphate synthetase (EC 2.7.2.5), ornithine transcarbamylase (EC 2.1.3.3), glutamate dehydrogenase (EC 1.4.1.3), pyruvate carboxylase (EC 6.4.1.1), citrate synthase (EC 4.1.3.7), fumarase (EC 4.2.1.2), aconitase (EC 4.2.1.3), alpha-ketoglutarate dehydrogenase (EC 1.2.4.2), dihydrolipoyl transsuccinylase (EC 2.3.1.12), lipoamide dehydrogenase (EC 1.6.4.3), glutamate-aspartate aminotransferase (EC 2.6.1.1), and the two subunits of pyruvate dehydrogenase (EC 1.2.4.1). Protein components unambiguously identified by peptide mapping are citrate synthase, aconitase, and pyruvate carboxylase. The inner membrane subfraction from rat liver mitochondria was also resolved two dimensionally; the alpha and beta subunits of ATPase (F1) (EC 3.6.1.3) were identified by peptide mapping.
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PMID:Resolution of rat mitochondrial matrix proteins by two-dimensional polyacrylamide gel electrophoresis. 44 63


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