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

---

Query: EC:1.6.99.3 (diaphorase)
5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A catalytic component of the bovine mitochondrial NADH:ubiquinone oxidoreductase complex (Complex I) is a soluble NADH dehydrogenase iron-sulfur flavoprotein (FP). FP is composed of three subunits of Mr 51,000, 24,000, and 9,000, and contains FMN and two iron-sulfur clusters. Previous studies by others with the use of various chemical probes had suggested that, except for an access for NADH to the 51-kDa subunit, the FP polypeptides are buried within Complex I and shielded from the medium. In the present study, monospecific antibodies were raised to each of the three FP subunits, and used in conjunction with Complex I, submitochondrial particles (SMP), mitoplasts, and intact mitochondria as sources of antigens. Results of enzyme-linked immunosorbent assays and 125I-protein A labeling experiments indicated that epitopes from the 51-, 24-, and 9-kDa subunits of FP are exposed to the medium in Complex I and SMP, but not in mitoplasts and mitochondria. Appropriate enzymatic assays showed that none of the antibodies inhibited the NADH dehydrogenase activity of isolated FP or the NADH oxidase activity of SMP. These results have been discussed in relation to the structure of Neurospora Complex I deduced from membrane crystals of the isolated enzyme complex by Leonard et al. [K. Leonard, H. Haiker, and H. Weiss (1987) J. Mol. Biol. 194, 277-286].
...
PMID:Studies on the structure of NADH:ubiquinone oxidoreductase complex: topography of the subunits of the iron-sulfur flavoprotein component. 246 82

1. An NADH-dependent nitroreductase from the inner membrane of ox liver mitochondria copurified with Complex I of the respiratory redox chain (NADH:ubiquinone oxidoreductase, EC 1.6.5.3). 2. The corresponding nitroreductase from ox heart mitochondria co-purified with the NADH-cytochrome c reductase of Mahler, Sarkar & Vernon [(1952) J. Biol. Chem. 199, 585-597] [NADH: (acceptor) oxidoreductase, EC 1.6.99.3], a component of Complex I that contains the FMN. 3. The mitochondrial nitroreductase activity is attributed to the flavoprotein component of Complex I.
...
PMID:Nitroreductase activity of NADH dehydrogenase of the respiratory redox chain. 249 90

Pituitary-determined hormones regulate the expression of hepatic cytochromes P-450 through processes involving both negative and positive controls. Accordingly, protein levels of several P-450 forms are elevated in rat liver following hypophysectomy [P-450 forms designated 2a (gene IIIA2), RLM2 (gene IIA2), and PB-4 (gene IIB1)], whereas protein levels of others are suppressed [e.g., P-450 2c (gene IIC11)]. In the present study, microsomal steroid hydroxylase activities associated with these same P-450 forms were found to be decreased by hypophysectomy, despite elevations in protein levels for several of them. Studies were, therefore, undertaken to determine the biochemical basis for this decrease in microsomal P-450 enzyme specific activity. In vivo treatment of hypophysectomized rats with gonadotropin, under conditions that restore heme to testis P-450, and heme reconstitution experiments carried out with liver homogenates indicated that a deficiency in P-450-associated heme is unlikely to account for the observed decreases in liver P-450 enzyme specific activity. Analysis of the flavoprotein P-450 reductase, however, revealed that the reductase protein and its associated cytochrome c reductase activity are decreased by 50 to 75% in liver microsomes isolated from hypophysectomized rats. Moreover, supplementation of isolated liver microsomes with exogenous purified P-450 reductase stimulated microsomal steroid hydroxylase activity preferentially in the hypophysectomized rats, to levels consistent with the observed changes in P-450 protein levels. Thus, a deficiency in P-450 reductase, which is a rate-limiting component for many P-450-dependent hydroxylation reactions, appears to be responsible for the decrease in steroid hydroxylase specific activity in the hypophysectomized rats. Although growth hormone, adrenocorticotropic hormone, and chorionic gonadotropin were each ineffective at restoring hepatic P-450 reductase when administered to hypophysectomized rats, substantial restoration of P-450 reductase levels could be achieved by treatment of the hypophysectomized rats with thyroxine. Thyroxine treatment of these rats also elevated the microsomal steroid hydroxylase activities associated with the individual hepatic P-450 forms to levels commensurate with their respective P-450 protein levels. These results establish that hepatic P-450 reductase is subject to hormonal controls that are distinct from those governing cytochrome P-450 expression and further demonstrate the complexity of endocrine control of hepatic steroid hormone metabolism.
...
PMID:Hypophysectomy differentially alters P-450 protein levels and enzyme activities in rat liver: pituitary control of hepatic NADPH cytochrome P-450 reductase. 249 35

The 24-kDa subunit of mitochondrial NADH-ubiquinone reductase (complex I) is an iron-sulfur protein that is present in the flavoprotein or NADH dehydrogenase II subcomplex. It is a nuclear gene product and is imported into the organelle. A group of human patients with mitochondrial myopathy have been shown to have reduced levels of subunits of complex I in skeletal muscle mitochondria, and in one patient the 24-kDa subunit appears to be absent (Schapira et al., 1988). To investigate the genetic basis of this type of myopathy, cDNA clones have been isolated from a bovine library derived from heart and liver mRNA by hybridization with two mixtures of 48 synthetic oligonucleotides 17 bases in length that were designed on the basis of known protein sequences. The recombinant DNA sequence has been determined, and it encodes a precursor of the mature 24-kDa protein. The N terminus of the mature protein is preceded by a presequence of 32 amino acids that has properties that are characteristic of mitochondrial import sequences. The sequence of the mature protein deduced from the cDNA contains a segment of nine amino acids that was not determined in an earlier partial protein sequence analysis. The bovine clone has been employed as a hybridization probe to identify cDNA clones of the human homologue of the 24-kDa protein. Its DNA sequence has also been determined, and it codes for a protein that is closely related to the bovine protein.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Mitochondrial NADH-ubiquinone reductase: complementary DNA sequences of import precursors of the bovine and human 24-kDa subunit. 250 Sep 70

Administration of purified bacterial lipopolysaccharide (LPS) to male rats suppressed the constitutive hepatic expression of the male-specific cytochrome P-450 [AH, reduced flavoprotein:oxygen oxidoreductase (RH hydroxylating), E.C.1.14.14.1] isozyme P-450h (P450IIC11) to about 35% of control levels within 24 hr. The mRNA for P-450h was more rapidly and more profoundly suppressed than was the protein, indicating (a) that the decrease in the mRNA was responsible for the suppression of the protein and (b) that other mechanisms work to maintain expression of P-450h apoprotein in the face of repression of its mRNA. Suppression of P-450h expression was maximal at an endotoxin dose of 30-100 micrograms/kg, indicating that P-450 suppression is concomitant with the acute-phase response of hepatic secretory proteins. The female-specific cytochrome P-450 isozyme, P-450i (P450IIC12), was suppressed to 17% of control levels by LPS administration in female rats. Suppression of the P-450i apoprotein by LPS, and recovery of its expression, was more rapid than was suppression of P-450h in males. P-450i protein and mRNA levels were concomitantly suppressed by LPS, indicating that although there is a pretranslational component to the suppression, other mechanisms may also contribute. Calculations based on estimations of the microsomal contents of P-450h and P-450i relative to the total cytochrome P-450 in untreated rat livers indicate that suppression of these forms contributes significantly to the decreases in total microsomal P-450 after LPS treatment. In these studies, hepatic microsomal NADPH-cytochrome c reductase (TPNH2-cytochrome c reductase, E.C.1.6.2.4) activities and content of cytochrome b5 were decreased by LPS administration in both male and female rats. Like its effects on cytochrome P-450 expression, endotoxin suppression of NADPH-cytochrome c reductase activities and cytochrome b5 levels was more rapid in female rats than in males. The production of a local inflammatory response in male rats by subcutaneous injection of turpentine caused effects on cytochrome P-450, P-450h expression, and cytochrome b5 that were similar to those of endotoxin but were less rapidly achieved.
...
PMID:Suppression of constitutive cytochrome P-450 gene expression in livers of rats undergoing an acute phase response to endotoxin. 251 27

NADPH-sulfite reductase flavoprotein (SiR-FP) was purified from a Salmonella typhimurium cysG strain that does not synthesize the hemoprotein component of the sulfite reductase holoenzyme. cysJ, which codes for SiR-FP, was cloned from S. typhimurium LT7 and Escherichia coli B, and both genes were sequenced. Physicochemical analyses and deduced amino acid sequences indicate that SiR-FP is an octamer of identical 66-kDa peptides and contains 4 FAD and 4 FMN per octamer. Potentiometric titrations of SiR holoenzyme, SiR-FP, and FMN-depleted SiR-FP yielded the following redox potentials for the prosthetic groups at pH 7.7: E'1 (FMNH./FMN) = -152 mV; E'2 (FMNH2/FMNH.) = -327 mV; E'3 (FADH./FAD) = -382 mV; E'4 (FADH2/FADH.) = -322 mV. Microcoulometric titration of SiR-FP at 25 degrees C yielded data which were in full agreement with these potentials. Spectroscopic and catalytic studies of native SiR-FP and of SiR-FP depleted of FMN support the following electron flow sequence: NADPH----FAD----FMN. FMN can then contribute electrons to the hemoprotein component of sulfite reductase, as well as to cytochrome c and various diaphorase acceptors. The FMN is postulated to cycle between the FMNH2 and FMNH. oxidation states during catalysis; in this sense SiR-FP shares a catalytic mechanism with NADPH-cytochrome P-450 oxidoreductase. SiR-FP domains involved in binding FMN, FAD, and NADPH are proposed from amino acid sequence homologies with Desulfovibrio vulgaris flavodoxin (Dubourdieu, M., and Fox, J.L. (1977) J. Biol. Chem. 252, 1453-1463) and spinach ferredoxin-NADP+ oxidoreductase (Karplus, P.A., Walsh, K.A., and Herriott, J. R. (1984) Biochemistry 23, 6576-6583). Comparison of the deduced amino acid sequences of SiR-FP and NADPH-cytochrome P-450 oxidoreductase (Porter, T. D., and Kasper, C.B. (1985) Proc. Natl. Acad. Sci. U. S.A. 82, 973-977) also showed identities that suggest these two proteins are descended from a common precursor, which contained binding regions for both FMN and FAD.
...
PMID:Characterization of the flavoprotein moieties of NADPH-sulfite reductase from Salmonella typhimurium and Escherichia coli. Physicochemical and catalytic properties, amino acid sequence deduced from DNA sequence of cysJ, and comparison with NADPH-cytochrome P-450 reductase. 255 Apr 23

Dopamine (DA) is rapidly oxidized by Mn3(+)-pyrophosphate to its cyclized o-quinone (cDAoQ), a reaction which can be prevented by NADH, reduced glutathione (GSH) or ascorbic acid. The oxidation of DA by Mn3+, which appears to be irreversible, results in a decrease in the level of DA, but not in a formation of reactive oxygen species, since oxygen is neither consumed nor required in this reaction. The formation of cDAoQ can initiate the generation of superoxide radicals (O2-.) by reduction-oxidation cycling, i.e. one-electron reduction of the quinone by various NADH- or NADPH-dependent flavoproteins to the semiquinone (QH.), which is readily reoxidized by O2 with the concomitant formation of O2-.. This mechanism is believed to underly the cytotoxicity of many quinones. Two-electron reduction of cDAoQ to the hydroquinone can be catalyzed by the flavoprotein DT diaphorase (NAD(P)H:quinone oxidoreductase). This enzyme efficiently maintains DA quinone in its fully reduced state, although some reoxidation of the hydroquinone (QH2) is observed (QH2 + O2----QH. + O2-. + H+; QH. + O2----Q + O2-.). In the presence of Mn3+, generated from Mn2+ by O2-. (Mn2+ + 2H+ + O2-.----Mn3+ + H2O2) formed during the autoxidation of DA hydroquinone, the rate of autoxidation is increased dramatically as is the formation of H2O2. Furthermore, cDAoQ is no longer fully reduced and the steady-state ratio between the hydroquinone and the quinone is dependent on the amount of DT diaphorase present. The generation of Mn3+ is inhibited by superoxide dismutase (SOD), which catalyzes the disproportionation of O2-. to H2O2 and O2. It is noteworthy that addition of SOD does not only result in a decrease in the amount of H2O2 formed during the regeneration of Mn3+, but, in fact, prevents H2O2 formation. Furthermore, in the presence of this enzyme the consumption of O2 is low, as is the oxidation of NADH, due to autoxidation of the hydroquinone, and the cyclized DA o-quinone is found to be fully reduced. These observations can be explained by the newly-discovered role of SOD as a superoxide:semiquinone (QH.) oxidoreductase catalyzing the following reaction: O2-. + QH. + 2H+----QH2 + O2. Thus, the combination of DT diaphorase and SOD is an efficient system for maintaining cDAoQ in its fully reduced state, a prerequisite for detoxication of the quinone by conjugation with sulfate or glucuronic acid. In addition, only minute amounts of reactive oxygen species will be formed, i.e. by the generation of O2-., which through disproportionation to H2O2 and further reduction by ferrous ions can be converted to the hydroxyl radical (OH.). Absence or low levels of these enzymes may create an oxidative stress on the cell and thereby initiate events leading to cell death.
...
PMID:On the mechanism of the Mn3(+)-induced neurotoxicity of dopamine:prevention of quinone-derived oxygen toxicity by DT diaphorase and superoxide dismutase. 255 82

Biosynthesis of ferredoxin-NADP+ reductase in higher plants was investigated in relation with the mechanism of formation of the holoenzyme. The putative precursor of the flavoprotein, obtained after cell-free translation on a wheat germ extract primed with poly(A)-rich mRNA, was able to spontaneously bind free FAD, rendering a functional prereductase. The newly synthesized preholoenzyme showed diaphorase and cytochrome c reductase activities, an apparent molecular mass of 45 kDa, and contained FAD as the only flavin cofactor. It gave a positive reaction towards antisera against mature ferredoxin-NADP+ reductase. On the other hand, intracellular distribution of flavin-synthesizing enzymes indicates that FAD formation occurs in the cytoplasm; that is, in the same compartment as the site of reductase synthesis. On the basis of the preceding data a model is presented for the biosynthesis of the enzyme in vivo, involving conjugation of the apoprotein with FAD in the cytoplasm, followed by transport of the preholoreductase across the chloroplast envelope to reach its final destiny in the thylakoid membrane.
...
PMID:Biosynthesis of ferredoxin-NADP+ oxidoreductase. Evidence for the formation of a functional preholoenzyme in the cytoplasmic compartment. 286 41

DT diaphorase [NAD(P)H:quinone oxidoreductase] activity was measured in subcellular fractions from homogenates of striatum, frontal cortex, hippocampus, cerebellum, hypothalamus and substantia nigra. This flavoprotein, which by definition oxidizes dihydronicotinamide adenine dinucleotide and dihydronicotinamide adenine dinucleotide phosphate at equal rates and is completely inhibited by 10(-5) M dicoumarol, was found to constitute 80-90% of the total dihydronicotinamide adenine dinucleotide- and dihydronicotinamide adenine dinucleotide phosphate-reductase activities in all brain regions studied. Antibodies raised against purified cytosolic DT diaphorase from the rat liver cross-reacted with the brain enzyme and inhibited soluble DT diaphorase from striatum and cerebellum to 80-90%. Immunohistochemical studies with the same antibodies demonstrated the occurrence of DT diaphorase immunoreactivity in a population of neurons in the substantia nigra and ventral tegmental area. In some neurons there was a colocalization of DT diaphorase and tyrosine hydroxylase-like immunoreactivity. The dense network of DT diaphorase-immunoreactive fibres in the striatum disappeared along with the dopaminergic innervation after 6-hydroxydopamine lesion. DT diaphorase immunoreactivity was also found in Bergmann glia, astrocytes and tanycytes. No correlation appeared to exist between the localization of neuronal DT diaphorase immunoreactivity and the dihydronicotinamide adenine dinucleotide phosphate-diaphorase-like activity, as defined by tetrazolium salt staining, used as a marker for certain peptidergic and cholinergic neurons. However, in, for example, glial cells in the cerebellum, DT diaphorase might contribute or be responsible for the histochemical dihydronicotinamide adenine dinucleotide phosphate-diaphorase activity.
...
PMID:Distribution of DT diaphorase in the rat brain: biochemical and immunohistochemical studies. 290 55

The influence of Ebselen, an organoselenium anti-inflammatory agent, on the two electron transport chains present in rat liver microsomes has been studied. At low micromolar concentrations, Ebselen markedly inhibited the flow of reducing equivalents from NADPH-cytochrome P450 reductase to both its natural electron acceptor, cytochrome P450, and its artificial electron acceptor, cytochrome c. Similarly, the microsomal NADH-cytochrome c reductase system consisting of cytochrome b5 and its flavoprotein, NADH-cytochrome b5 reductase, was also significantly inhibited by Ebselen. The inhibition appears to be due to the inability of the reduced pyridine nucleotide to transfer electrons to the flavin (FAD and/or FMN) in the flavoprotein reductase. This was shown with the purified NADPH-cytochrome P450 reductase, which in the presence of Ebselen was not converted to the semiquinone form following the addition of NADPH. The addition of Ebselen to a suspension of hepatic microsomes from either untreated or phenobarbital-treated rats did not result in any spectral change characteristic of type I, type II, or reverse type I.
...
PMID:Disruption of rat hepatic microsomal electron transport chains by the selenium-containing anti-inflammatory agent Ebselen. 291 42


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---