Pulsed differential reactors and their use for kinetic studies of gas–solid reactions—application to mechanistic studies of the reactions of hydrogen sulfide and the alkaline minerals in coal

1979 ◽  
Vol 50 (1) ◽  
pp. 111-117 ◽  
Author(s):  
A. Attar
Keyword(s):  
Hydrogen Sulfide ◽  
Kinetic Studies ◽  
Mechanistic Studies

scholarly journals Aspartate or arginine? Validated redox state X-ray structures elucidate mechanistic subtleties of FeIV = O formation in bacterial dye-decolorizing peroxidases

2021 ◽  
Vol 26 (7) ◽  
pp. 743-761
Author(s):  
Marina Lučić ◽  
Michael T. Wilson ◽  
Dimitri A. Svistunenko ◽  
Robin L. Owen ◽  
Michael A. Hough ◽  
...  
Keyword(s):  
Redox State ◽  
Kinetic Studies ◽  
Site Directed Mutagenesis ◽  
X Rays ◽  
Mechanistic Studies ◽  
X Ray ◽  
X Ray Crystallography ◽  
Structural Framework ◽  
Solvent Isotope ◽  
Heme Peroxidases

AbstractStructure determination of proteins and enzymes by X-ray crystallography remains the most widely used approach to complement functional and mechanistic studies. Capturing the structures of intact redox states in metalloenzymes is critical for assigning the chemistry carried out by the metal in the catalytic cycle. Unfortunately, X-rays interact with protein crystals to generate solvated photoelectrons that can reduce redox active metals and hence change the coordination geometry and the coupled protein structure. Approaches to mitigate such site-specific radiation damage continue to be developed, but nevertheless application of such approaches to metalloenzymes in combination with mechanistic studies are often overlooked. In this review, we summarize our recent structural and kinetic studies on a set of three heme peroxidases found in the bacterium Streptomyces lividans that each belong to the dye decolourizing peroxidase (DyP) superfamily. Kinetically, each of these DyPs has a distinct reactivity with hydrogen peroxide. Through a combination of low dose synchrotron X-ray crystallography and zero dose serial femtosecond X-ray crystallography using an X-ray free electron laser (XFEL), high-resolution structures with unambiguous redox state assignment of the ferric and ferryl (FeIV = O) heme species have been obtained. Experiments using stopped-flow kinetics, solvent-isotope exchange and site-directed mutagenesis with this set of redox state validated DyP structures have provided the first comprehensive kinetic and structural framework for how DyPs can modulate their distal heme pocket Asp/Arg dyad to use either the Asp or the Arg to facilitate proton transfer and rate enhancement of peroxide heterolysis. Graphic abstract

scholarly journals Production of the Neuromodulator H2S by Cystathionine β-Synthase via the Condensation of Cysteine and Homocysteine

2004 ◽  
Vol 279 (50) ◽  
pp. 52082-52086 ◽  
Author(s):  
Xulin Chen ◽  
Kwang-Hwan Jhee ◽  
Warren D. Kruger
Keyword(s):  
Hydrogen Sulfide ◽  
Kinetic Studies ◽  
Mammalian Brain ◽  
Replacement Reaction ◽  
Elimination Kinetic ◽  
Major Mechanism ◽  
High Concentrations ◽  
Hydrolysis Of

Hydrogen sulfide (H2S) has been observed in relatively high concentrations in the mammalian brain and has been shown to act as a neuromodulator. However, there is confusion in the literature regarding the actual source of H2S production. Reactions catalyzed by the cystathionine β-synthase enzyme (CBS) are one possible source for the production of H2S. Here we show that the CBS enzyme can efficiently produce H2S via a β-replacement reaction in which cysteine is condensed with homocysteine to form cystathionine and H2S. The production of H2S by this reaction is at least 50 times more efficient than that produced by hydrolysis of cysteine alone via β-elimination. Kinetic studies demonstrate that theKmandKcatfor cysteine is 3-fold higher and 2-fold lower, respectively, than that for serine. Consistent with these data,in vitroreconstitution studies show that at physiologically relevant concentrations of serine, homocysteine, and cysteine, about 5% of the cystathionine formed is from cysteine. We also show that AdoMet stimulates this H2S producing reaction but that there is no evidence for stimulation by calcium and calmodulin as reported previously. In summary, these results confirm the ability of CBS to produce H2S, but show in contrast to prior reports that the major mechanism is via β-replacement and not cysteine hydrolysis. In addition, these studies provide a biochemical explanation for the previously inexplicable homocysteine-lowering effects ofN-acetylcysteine treatments in humans.

Kinetic studies of peroxiredoxin 6 from Arenicola marina: Rapid oxidation by hydrogen peroxide and peroxynitrite but lack of reduction by hydrogen sulfide

2011 ◽  
Vol 514 (1-2) ◽  
pp. 1-7 ◽  
Author(s):  
Eléonore Loumaye ◽  
Gerardo Ferrer-Sueta ◽  
Beatriz Alvarez ◽  
Jean-François Rees ◽  
André Clippe ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Hydrogen Sulfide ◽  
Kinetic Studies ◽  
Peroxiredoxin 6 ◽  
Arenicola Marina ◽  
Oxidation By Hydrogen Peroxide

Hierarchical silica monoliths with submicron macropores as continuous-flow microreactors for reaction kinetic and mechanistic studies in heterogeneous catalysis

2018 ◽  
Vol 3 (3) ◽  
pp. 353-364 ◽  
Author(s):  
Richard Kohns ◽  
Christian P. Haas ◽  
Alexandra Höltzel ◽  
Christian Splith ◽  
Dirk Enke ◽  
...  
Keyword(s):  
Heterogeneous Catalysis ◽  
Continuous Flow ◽  
Reaction Kinetic ◽  
Kinetic Studies ◽  
Mechanistic Studies ◽  
Silica Monoliths ◽  
Flow Microreactors

The proposed scheme enables academic laboratories to prepare hierarchical silica monoliths as continuous-flow microreactors for kinetic studies in heterogeneous catalysis.

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