Publications

• Characterization and partial purification of microsomal NAD(P)H:quinone oxidoreductases.

  Jaiswal A.K.

  Quinone oxidoreductases are flavoproteins that catalyze two-electron reduction and detoxification of quinones. This leads to the protection of cells against toxicity, mutagenicity, and cancer due to exposure to environmental and synthetic quinones and its precursors. Two cytosolic forms of quinone ... >> More

  Quinone oxidoreductases are flavoproteins that catalyze two-electron reduction and detoxification of quinones. This leads to the protection of cells against toxicity, mutagenicity, and cancer due to exposure to environmental and synthetic quinones and its precursors. Two cytosolic forms of quinone oxidoreductases [NAD(P)H:quinone oxidoreductase 1 (NQO1) and NRH:quinone oxidoreductase 2 (NQO2)] were previously identified, purified, and cloned. A role of cytosolic NQO1 in protection of cells from oxidative stress, cytotoxicity, and mutagenicity of quinones was established. Currently, we have characterized and partially purified the NQO activity from rat liver microsomes. This activity was designated as microsomal NQO (mNQO). The mNQO activity showed significantly higher affinity for NADH than NADPH as electron donors and catalyzed reduction of 2,6-dichlorophenolindophenol and menadione. The mNQO activity was insensitive to dicoumarol, a potent inhibitor of cytosolic NQO1. Western analysis of microsomal proteins revealed 29- and 18-kDa bands that cross-reacted with polyclonal antibodies raised against cytosolic NQO1. The mNQO activity was partially purified by solubilization of microsomes with detergent Chaps, ammonium sulfate fractionation, and DEAE-Sephacel column chromatography. The microsomal mNQO proteins are expected to provide additional protection after cytosolic NQOs against quinone toxicity and mutagenicity. << Less

  Arch Biochem Biophys 375:62-68(2000) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Characterization of the overproduced NADH dehydrogenase fragment of the NADH:ubiquinone oxidoreductase (complex I) from Escherichia coli.

  Braun M., Bungert S., Friedrich T.

  The proton-pumping NADH:ubiquinone oxidoreductase of Escherichia coli is composed of 14 different subunits and contains one FMN and up to nine iron-sulfur clusters as prosthetic groups. By use of salt treatment, the complex can be split into an NADH dehydrogenase fragment, a connecting fragment an ... >> More

  The proton-pumping NADH:ubiquinone oxidoreductase of Escherichia coli is composed of 14 different subunits and contains one FMN and up to nine iron-sulfur clusters as prosthetic groups. By use of salt treatment, the complex can be split into an NADH dehydrogenase fragment, a connecting fragment and a membrane fragment. The water-soluble NADH dehydrogenase fragment has a molecular mass of approximately 170,000 Da and consists of the subunits NuoE, F, and G. The fragment harbors the FMN and probably six iron-sulfur clusters, four of them being observable by EPR spectroscopy. Here, we report that the fully assembled fragment can be overproduced in E. coli when the genes nuoE, F, and G were simultaneously overexpressed with the genes nuoB, C, and D. Furthermore, riboflavin, sodium sulfide, and ferric ammonium citrate have to be added to the culture medium. The fragment was purified from the cytoplasm by means of ammonium sulfate fractionation and chromatographic steps. The preparation contains one noncovalently bound FMN per molecule. Two binuclear (N1b and N1c) and two tetranuclear (N3 and N4) iron-sulfur clusters were detected by EPR in the NADH reduced preparation with spectral characteristics identical with those of the corresponding clusters in complex I. The preparation fulfills all prerequisites for crystallization of the fragment. << Less

  Biochemistry 37:1861-1867(1998) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Effects of weight cycling on metabolic control in male outpatients with non-insulin-dependent diabetes mellitus.

  Schotte D.E., Cohen E., Singh S.P.

  Examined the effects of weight cycling (i.e., losing and regaining or gaining and relosing body weight) versus weight maintenance on metabolic control in 327 adult, male, outpatient veterans with non-insulin-dependent diabetes mellitus (NIDDM) who were followed over an average of 3.4 years. When c ... >> More

  Examined the effects of weight cycling (i.e., losing and regaining or gaining and relosing body weight) versus weight maintenance on metabolic control in 327 adult, male, outpatient veterans with non-insulin-dependent diabetes mellitus (NIDDM) who were followed over an average of 3.4 years. When compared with weight maintenance, weight cycling, whether defined as a categorical or as a continuous variable, was not found to be associated with deficits in metabolic control or increased need for hypoglycemic medication. Patients who weight cycled had fasting serum glucose and hemoglobin A1c levels comparable to those who remained within 10% of their initial body weights, and these levels of metabolic control were obtained with similar classes and dosages of hypoglycemic medication. << Less

  Health Psychol 9:599-605(1990) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• The three-dimensional structure of NAD(P)H:quinone reductase, a flavoprotein involved in cancer chemoprotection and chemotherapy: mechanism of the two-electron reduction.

  Li R., Bianchet M.A., Talalay P., Amzel L.M.

  Quinone reductase [NAD(P)H:(quinone acceptor) oxidoreductase, EC 1.6.99.2], also called DT diaphorase, is a homodimeric FAD-containing enzyme that catalyzes obligatory NAD(P)H-dependent two-electron reductions of quinones and protects cells against the toxic and neoplastic effects of free radicals ... >> More

  Quinone reductase [NAD(P)H:(quinone acceptor) oxidoreductase, EC 1.6.99.2], also called DT diaphorase, is a homodimeric FAD-containing enzyme that catalyzes obligatory NAD(P)H-dependent two-electron reductions of quinones and protects cells against the toxic and neoplastic effects of free radicals and reactive oxygen species arising from one-electron reductions. These two-electron reductions participate in the reductive bioactivation of cancer chemotherapeutic agents such as mitomycin C in tumor cells. Thus, surprisingly, the same enzymatic reaction that protects normal cells activates cytotoxic drugs used in cancer chemotherapy. The 2.1-A crystal structure of rat liver quinone reductase reveals that the folding of a portion of each monomer is similar to that of flavodoxin, a bacterial FMN-containing protein. Two additional portions of the polypeptide chains are involved in dimerization and in formation of the two identical catalytic sites to which both monomers contribute. The crystallographic structures of two FAD-containing enzyme complexes (one containing NADP+, the other containing duroquinone) suggest that direct hydride transfers from NAD(P)H to FAD and from FADH2 to the quinone [which occupies the site vacated by NAD(P)H] provide a simple rationale for the obligatory two-electron reductions involving a ping-pong mechanism. << Less

  Proc. Natl. Acad. Sci. U.S.A. 92:8846-8850(1995) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.