H-1, N-15 and C-13 backbone resonance assignments of pentaerythritol tetranitrate reductase from Enterobacter cloacae PB2

Pentaerythritol tetranitrate reductase (PETNR) is a flavoenzyme possessing a broad substrate specificity and is a member of the Old Yellow Enzyme family of oxidoreductases. As well as having high potential as an industrial biocatalyst, PETNR is an excellent model system for studying hydrogen transfer reactions. Mechanistic studies performed with PETNR using stopped-flow methods have shown that tunneling contributes towards hydride transfer from the NAD(P)H coenzyme to the flavin mononucleotide (FMN) cofactor and fast protein dynamics have been inferred to facilitate this catalytic step. Herein, we report the near-complete 1H, 15N and 13C backbone resonance assignments of PETNR in a stoichiometric complex with the FMN cofactor in its native oxidized form, which were obtained using heteronuclear multidimensional NMR spectroscopy. A total of 97% of all backbone resonances were assigned, with 333 out of a possible 344 residues assigned in the 1H–15N TROSY spectrum. This is the first report of an NMR structural study of a flavoenzyme from the Old Yellow Enzyme family and it lays the foundation for future investigations of functional dynamics in hydride transfer catalytic mechanism

Modification of acid-base properties of TiO₂ by Nb and Mg dopants:Influence on the activity of Pd-Cu/(Mg, Nb)-TiO2 catalysts for nitrate hydrogenation

MATERIAUX+NBO:AIO:SDA:NOGInternational audienceThe influence of the acid-base properties of TiO2-based supports on the performances of Pd-Cu bimetallic catalysts for the hydrogenation of nitrates in water has been investigated. Nanostructured TiO2 and TiO2 doped with various amounts of Mg and Nb (1-7 wt%) were prepared by co-hydrolysis of metal alkoxides. The surface area increased and the crystallinity decreased for Mg- and Nb-doped TiO2, all solids exhibiting mesoporosity with average pore sizes smaller than 20 nm. The acid-base properties of TiO2 were strongly modified by doping, Mg introducing a basic character whereas Nb-doped TiO2 becomes acidic. Pd-Cu bimetallic catalysts deposited on TiO2 and Mg- or Nb-doped TiO2 were found very active for the catalytic hydrogenation of nitrates, but the selectivity to ammonium was high. Nb-doping slightly decreased the reactivity of nitrates and Mg-doping slightly improved the reactivity of nitrites, whereas the selectivity to ammoniums was only marginally modified. The activity and products selectivity were very moderately affected by the acid or basic character of the support, which suggests that this property is not relevant to the reaction mechanism. (C) 2013 Elsevier B.V. All rights reserved

Solution-State Inter-Copper Distribution of Redox Partner-Linked Copper Nitrite Reductases: A Pulsed Electron–Electron Double Resonance Spectroscopy Study

[Image: see text] Copper nitrite reductases (CuNiRs) catalyze the reduction of nitrite to form nitric oxide. In recent years, new classes of redox partner linked CuNiRs have been isolated and characterized by crystallographic techniques. Solution-state biophysical studies have shed light on the complex catalytic mechanisms of these enzymes and implied that protein dynamics may play a role in CuNiR catalysis. To investigate the structural, dynamical, and functional relationship of these CuNiRs, we have used protein reverse engineering and pulsed electron–electron double resonance (PELDOR) spectroscopy to determine their solution-state inter-copper distributions. Data show the multidimensional conformational landscape of this family of enzymes and the role of tethering in catalysis. The importance of combining high-resolution crystallographic techniques and low-resolution solution-state approaches in determining the structures and mechanisms of metalloenzymes is emphasized by our approach