The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Vincent Massey - One of the best experts on this subject based on the ideXlab platform.
-
the chemical and biological versatility of riboflavin
Biochemical Society Transactions, 2000Co-Authors: Vincent MasseyAbstract:Since their discovery and chemical characterization in the 1930s, flavins have been recognized as being capable of both one- and two-electron transfer processes, and as playing a pivotal role in coupling the two-electron oxidation of most organic substrates to the one-electron transfers of the respiratory chain. In addition, they are now known as versatile compounds that can function as electrophiles and nucleophiles, with covalent intermediates of flavin and substrate frequently being involved in catalysis. Flavins are thought to contribute to oxidative stress through their ability to produce superoxide, but at the same time flavins are frequently involved in the reduction of hydroperoxides, products of oxygen-derived radical reactions. Flavoproteins play an important role in soil detoxification processes via the hydroxylation of many aromatic compounds, and a simple Flavoprotein in liver microsomes catalyses many reactions similar to those carried out by cytochrome P450 enzymes. Flavins are involved in the production of light in bioluminescent bacteria, and are intimately connected with light-initiated reactions such as plant phototropism and nucleic acid repair processes. Recent reports also link them to programmed cell death. The chemical versatility of Flavoproteins is clearly controlled by specific interactions with the proteins with which they are bound. One of the main thrusts of current research is to try to define the nature of these interactions, and to understand in chemical terms the various steps involved in catalysis by Flavoprotein enzymes.
-
amphibacillus xylanus nadh oxidase and salmonella typhimurium alkyl hydroperoxide reductase Flavoprotein components show extremely high scavenging activity for both alkyl hydroperoxide and hydrogen peroxide in the presence of s typhimurium alkyl hydr
Journal of Biological Chemistry, 1995Co-Authors: Youichi Niimura, Leslie B Poole, Vincent MasseyAbstract:The Flavoprotein NADH oxidase from Amphibacillus xylanus consumes oxygen to produce hydrogen peroxide. The amino acid sequence of this Flavoprotein shows 51.2% identity to the F-52a component, denoted AhpF, of the alkyl-hydroperoxide reductase from Salmonella typhimurium. AhpF also catalyzes NADH-dependent hydrogen peroxide formation under aerobic conditions, albeit at a somewhat slower rate than the Amphibacillus protein. In the presence of the 22-kDa colorless component (AhpC) of the Salmonella alkyl-hydroperoxide reductase, both proteins catalyze the 4-electron reduction of oxygen to water. Both Flavoproteins are active as AhpC reductases and mediate electron transfer, resulting in the NADH-dependent reduction of hydrogen peroxide and cumene hydroperoxide. Both enzymes' Km values for hydrogen peroxide, cumene hydroperoxide, and NADH are so low that they could not be determined accurately. Vmax values for hydrogen peroxide or cumene hydroperoxide reduction are > 10,000 min(-1) at 25 degrees C. These values are almost the same as the reduction rate of the Flavoprotein component by NADH. The involvement in catalysis of a redox-active disulfide of the A. xylanus Flavoprotein was shown by construction of three mutant enzymes, C337S, C340S, and C337S/C40SC337S/C340S. Very little activity for hydrogen peroxide or cumene hydroperoxide was found with the single mutants (C337S and C340S), and none with the double mutant (C337S/C340S). Analysis of the DNA sequence upstream of the Amphibacillus Flavoprotein structural gene indicated the presence of a partial open reading frame homologous to the Salmonella ahpC structural gene (64.3% identical at the amino acid sequence level), suggesting that the NADH oxidase protein of A. xylanus is also part of a functional alkyl-hydroperoxide reductase system within these catalase-lacking bacteria.
Alain Virion - One of the best experts on this subject based on the ideXlab platform.
-
expression of reduced nicotinamide adenine dinucleotide phosphate oxidase thox lnox duox genes and proteins in human thyroid tissues
The Journal of Clinical Endocrinology and Metabolism, 2001Co-Authors: Bernard Caillou, Renée Ohayon, Corinne Dupuy, Danielle Dème, Ludovic Lacroix, Maria Nocera, Monique Talbot, Jeanmichel Bidart, Martin Schlumberger, Alain VirionAbstract:The large homolog of NADPH oxidase Flavoprotein LNOX2, and probably LNOX1, are Flavoproteins involved in the thyroid H2O2 generator. Western blot analysis of membrane proteins from normal human thyroid, using antipeptide antibodies, indicated that LNOX1,2 are 164-kDa glycoproteins and that N-glycosylated motifs account for at least 10–20 kDa of their total apparent molecular mass. Northern blot analysis of 23 different human tissues demonstrated that LNOX2 messenger RNA (mRNA) is strongly expressed only in the thyroid gland, although blast analysis of expressed sequence tags databases indicated that LNOX genes are also expressed in some nonthyroid cells. We investigated LNOX1,2 gene and protein expressions in normal and pathological human thyroid tissues using real-time kinetic quantitative PCR and antipeptide antibodies, respectively. In normal tissue, LNOX1,2 are localized at the apical pole of thyrocytes. Immunostaining for LNOX1,2 was heterogeneous, inside a given follicle, with 40–60% of positive fol...
-
Thyroid oxidase (THOX2) gene expression in the rat thyroid cell line FRTL-5.
Biochemical and biophysical research communications, 2000Co-Authors: Corinne Dupuy, Renée Ohayon, Marie-sophie Noel-hudson, Martine Pomerance, Danielle Dème, Mokhtar Chaaraoui, Jacques Francon, Alain VirionAbstract:A cDNA encoding an NADPH oxidase Flavoprotein was isolated from the rat thyroid gland. The predicted 1517-residue polypeptide was 82.5% identical to the human THOX2/DUOX2 and 74% similar to THOX1/DUOX1. Rat THOX2 lacks a stretch of 30 residues, corresponding to one exon in the human gene sequence. THOX2 mRNA was found to be expressed in cultured FRTL-5 cells. The level of THOX2 mRNA was increased by cAMP in these cells and it was decreased in the thyroids of rats treated with the antithyroid drug methimazole, unlike the TPO and NIS mRNAs. Since it was found in the intestine, duodenum, and colon, in addition to thyroid, we suggest that it be called LNOX, the new family of long homologs of NOX Flavoproteins rather than THOX and/or DUOX.
Koichiro Takeshige - One of the best experts on this subject based on the ideXlab platform.
-
cytochrome b558 a flavocytochrome comprising the complete electron transporting apparatus of phagocyte nadph oxidase
Stem Cells, 1994Co-Authors: Hideki Sumimoto, Koichiro TakeshigeAbstract:The microbicidal oxidase of phagocytes, upon activation, reduces molecular oxygen to superoxide in conjunction with the oxidation of reduced nicotinamide adenine dinucleotide phosphate (NADPH). The terminal component of the oxidative cascade is cytochrome b558 consisting of 91 kDa (gp91-phox) and 22 kDa (p22-phox) subunits with heme acting as the electron carrier to oxygen. However, the NADPH-binding Flavoprotein that transports electrons from the substrate to the cytochrome has not been identified. Alignment of the amino acid sequence of gp91-phox with that of previously characterized Flavoproteins suggests that this subunit contains both the NADPH-and flavin adenine dinucleotide (FAD)-binding domains. Several lines of experimental evidence strongly support this proposal. Thus cytochrome b558 is regarded as the first example of a flavocytochrome in higher eukaryotes, comprising the complete electron transporting machinery of phagocyte NADPH oxidase.
-
Cytochrome b558: A flavocytochrome comprising the complete electron‐transporting apparatus of phagocyte NADPH oxidase
Stem Cells, 1994Co-Authors: Hideki Sumimoto, Koichiro TakeshigeAbstract:The microbicidal oxidase of phagocytes, upon activation, reduces molecular oxygen to superoxide in conjunction with the oxidation of reduced nicotinamide adenine dinucleotide phosphate (NADPH). The terminal component of the oxidative cascade is cytochrome b558 consisting of 91 kDa (gp91-phox) and 22 kDa (p22-phox) subunits with heme acting as the electron carrier to oxygen. However, the NADPH-binding Flavoprotein that transports electrons from the substrate to the cytochrome has not been identified. Alignment of the amino acid sequence of gp91-phox with that of previously characterized Flavoproteins suggests that this subunit contains both the NADPH-and flavin adenine dinucleotide (FAD)-binding domains. Several lines of experimental evidence strongly support this proposal. Thus cytochrome b558 is regarded as the first example of a flavocytochrome in higher eukaryotes, comprising the complete electron transporting machinery of phagocyte NADPH oxidase.
-
Cytochrome b558, a component of the phagocyte NADPH oxidase, is a Flavoprotein.
Biochemical and Biophysical Research Communications, 1992Co-Authors: Hideki Sumimoto, Norihiro Sakamoto, Masahiko Nozaki, Koichiro Takeshige, Yoshiyuki Sakaki, Shigeki MinakamiAbstract:Cytochrome b 558 is the only membrane component of the phagocyte O 2 − NADPH oxidase. The O 2 − production by the oxidase reconstituted in vitro with the crude membrane fraction is enhanced several-fold by addition of FAD, whereas that with the partially purified cytochrome is completely dependent on exogenous FAD, suggesting that FAD acts through the membrane component, cytochrome b 558 . The alignments of the amino acid sequence of the large subunit of the cytochrome (gp91- phox ) with those of previously characterized Flavoproteins reveal that the middle and C-terminal portions of gp91- phox are likely to be FAD- and NADPHbinding domains, respectively. Cytochrome b 558 , thus, appears to be a Flavoprotein with an NADPH-binding site, of the NADPH oxidase.
Youichi Niimura - One of the best experts on this subject based on the ideXlab platform.
-
amphibacillus xylanus nadh oxidase and salmonella typhimurium alkyl hydroperoxide reductase Flavoprotein components show extremely high scavenging activity for both alkyl hydroperoxide and hydrogen peroxide in the presence of s typhimurium alkyl hydr
Journal of Biological Chemistry, 1995Co-Authors: Youichi Niimura, Leslie B Poole, Vincent MasseyAbstract:The Flavoprotein NADH oxidase from Amphibacillus xylanus consumes oxygen to produce hydrogen peroxide. The amino acid sequence of this Flavoprotein shows 51.2% identity to the F-52a component, denoted AhpF, of the alkyl-hydroperoxide reductase from Salmonella typhimurium. AhpF also catalyzes NADH-dependent hydrogen peroxide formation under aerobic conditions, albeit at a somewhat slower rate than the Amphibacillus protein. In the presence of the 22-kDa colorless component (AhpC) of the Salmonella alkyl-hydroperoxide reductase, both proteins catalyze the 4-electron reduction of oxygen to water. Both Flavoproteins are active as AhpC reductases and mediate electron transfer, resulting in the NADH-dependent reduction of hydrogen peroxide and cumene hydroperoxide. Both enzymes' Km values for hydrogen peroxide, cumene hydroperoxide, and NADH are so low that they could not be determined accurately. Vmax values for hydrogen peroxide or cumene hydroperoxide reduction are > 10,000 min(-1) at 25 degrees C. These values are almost the same as the reduction rate of the Flavoprotein component by NADH. The involvement in catalysis of a redox-active disulfide of the A. xylanus Flavoprotein was shown by construction of three mutant enzymes, C337S, C340S, and C337S/C40SC337S/C340S. Very little activity for hydrogen peroxide or cumene hydroperoxide was found with the single mutants (C337S and C340S), and none with the double mutant (C337S/C340S). Analysis of the DNA sequence upstream of the Amphibacillus Flavoprotein structural gene indicated the presence of a partial open reading frame homologous to the Salmonella ahpC structural gene (64.3% identical at the amino acid sequence level), suggesting that the NADH oxidase protein of A. xylanus is also part of a functional alkyl-hydroperoxide reductase system within these catalase-lacking bacteria.
Giovanni Gadda - One of the best experts on this subject based on the ideXlab platform.
-
Role of Valine 464 in the Flavin Oxidation Reaction Catalyzed by Choline Oxidase
Biochemistry, 2010Co-Authors: Steffan Finnegan, Irene T Weber, Johnson Agniswamy, Giovanni GaddaAbstract:The oxidation of reduced flavin cofactors by oxygen is a very important reaction that is central to the chemical versatility of hundreds of Flavoproteins classified as monooxygenases and oxidases. These enzymes are characterized by bimolecular rate constants ≥105 M−1 s−1 and produce water and hydrogen peroxide, respectively. A hydrophobic cavity close to the reactive flavin C(4a) atom has been previously identified in the 3D structure of monooxygenases but not in Flavoprotein oxidases. In the present study, we have investigated by X-ray crystallography, mutagenesis, steady-state, and rapid reaction approaches the role of Val464, which is
-
role of valine 464 in the flavin oxidation reaction catalyzed by choline oxidase
Biochemistry, 2010Co-Authors: Steffan Finnegan, Irene T Weber, Johnson Agniswamy, Giovanni GaddaAbstract:The oxidation of reduced flavin cofactors by oxygen is a very important reaction that is central to the chemical versatility of hundreds of Flavoproteins classified as monooxygenases and oxidases. These enzymes are characterized by bimolecular rate constants ≥105 M−1 s−1 and produce water and hydrogen peroxide, respectively. A hydrophobic cavity close to the reactive flavin C(4a) atom has been previously identified in the 3D structure of monooxygenases but not in Flavoprotein oxidases. In the present study, we have investigated by X-ray crystallography, mutagenesis, steady-state, and rapid reaction approaches the role of Val464, which is <6 A from the flavin C(4a) atom in choline oxidase. The 3D structure of the Val464Ala enzyme was essentially identical to that of the wild-type enzyme as shown by X-ray crystallography. Time-resolved anaerobic substrate reduction of the enzymes showed that replacement of Val464 with alanine or threonine did not affect the reductive half-reaction. Steady-state and rapid ki...
