Radical-mediated dehydration reactions in anaerobic bacteria

2005 ◽  
Vol 386 (10) ◽  
pp. 951-959 ◽  
Author(s):  
Wolfgang Buckel ◽  
Berta M. Martins ◽  
Albrecht Messerschmidt ◽  
Bernard T. Golding
Keyword(s):  
Radical Anion ◽  
Anaerobic Bacteria ◽  
Basic Amino Acid ◽  
Hydroxyl Group ◽  
Reductive Activation ◽  
Ketyl Radical ◽  
Dehydration Reactions ◽  
Amino Acid Side Chains ◽  
Acyl Coa Dehydrogenases ◽  
Electron Transfers

AbstractMost dehydratases catalyse the elimination of water from β-hydroxy ketones, β-hydroxy carboxylic acids or β-hydroxyacyl-CoA. The electron-withdrawing carbonyl functionalities acidify the α-hydrogens to enable their removal by basic amino acid side chains. Anaerobic bacteria, however, ferment amino acids via α- or γ-hydroxyacyl-CoA, dehydrations of which involve the abstraction of a β-hydrogen, which is ostensibly non-acidic (pKca. 40). Evidence is accumulating that β-hydrogens are acidified via transient conversion of the CoA derivatives to enoxy radicals by one-electron transfers, which decrease the pKto 14. The dehydrations of (R)-2-hydroxyacyl-CoA to (E)-2-enoyl-CoA are catalysed by heterodimeric [4Fe-4S]-containing dehydratases, which require reductive activation by an ATP-dependent one-electron transfer mediated by a homodimeric protein with a [4Fe-4S] cluster between the two subunits. The electron is further transferred to the substrate, yielding a ketyl radical anion, which expels the hydroxyl group and forms an enoxy radical. The dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA involves a similar mechanism, in which the ketyl radical anion is generated by one-electron oxidation. The structure of the FAD- and [4Fe-4S]-containing homotetrameric dehydratase is related to that of acyl-CoA dehydrogenases, suggesting a radical-based mechanism for both flavoproteins.

scholarly journals Erratum: Basic amino-acid side chains regulate transmembrane integrin signalling

Nature ◽  
2013 ◽  
Vol 497 (7451) ◽  
pp. 652-652
Author(s):  
Chungho Kim ◽  
Thomas Schmidt ◽  
Eun-Gyung Cho ◽  
Feng Ye ◽  
Tobias S. Ulmer ◽  
...  
Keyword(s):  
Amino Acid ◽  
Basic Amino Acid ◽  
Side Chains ◽  
Amino Acid Side Chains

Hammett-Streitwieser Reaction Constants for the Electroreduction of Diaryl Ketones in Aprotic Media

1996 ◽  
Vol 49 (8) ◽  
pp. 901 ◽  
Author(s):  
E Wagnerczauderna ◽  
MK Kalinowski
Keyword(s):  
Cyclic Voltammetry ◽  
Dimethyl Sulfoxide ◽  
Propylene Carbonate ◽  
Radical Anion ◽  
Electrode Reaction ◽  
Hexamethylphosphoric Triamide ◽  
Ketyl Radical ◽  
Donor Numbers ◽  
Reaction Constants ◽  
Solvent Acidity

Cyclic voltammetry has been used to measure formal potentials of seven aromatic ketone/ketyl radical anion systems in benzonitrile, acetonitrile , propylene carbonate, acetone, N,N- dimethylformamide, N-methylpyrrolidin-2-one, dimethyl sulfoxide and hexamethylphosphoric triamide. The values measured in each solvent obey the Hammett- Streitwieser equation; the reaction constants were found to depend on the solvent acidity and basicity expressed by acceptor and donor numbers, respectively. The results are discussed in terms of the solvation of the products and reactants of the electrode reaction.

Mechanism of the Electrochemical Carboxylation of Aromatic Ketones in Dimethylformamide

2003 ◽  
Vol 68 (8) ◽  
pp. 1379-1394 ◽  
Author(s):  
Abdirisak A. Isse ◽  
Armando Gennaro
Keyword(s):  
Radical Anion ◽  
Reduction Process ◽  
Kinetic Control ◽  
Peak Potential ◽  
Ketyl Radical ◽  
Aromatic Ketones ◽  
Experimental Parameters ◽  
Scan Rate ◽  
Kinetics Of ◽  
Electrochemical Carboxylation

The mechanism of the electrochemical carboxylation of several benzophenones (X-C6H4COC6H5; X = 4-OCH3, 4-CH3, H, 3-Cl, 3-CF3, 4-CF3 and 4-CN) and several ring-substituted acetophenones (Y-C6H4COCH3; Y = 4-OCH3, H, 3-OCH3, 3-Cl, 3-CF3, 4-CF3, 3-CN and 4-CN) has been investigated by cyclic voltammetry in dimethylformamide. In the presence of CO2, all compounds exhibit a single irreversible peak representing a 2 e reduction process. The reaction mechanism has been analysed using the dependence of the peak potential Ep on various experimental parameters such as the concentrations of the reactant, the scan rate and the temperature. Also the kinetics of the electrocarboxylation reaction has been examined. The whole set of results has been carefully analysed in the framework of an ECE-DISP mechanism. It has been found that, under the conditions employed, the electrocarboxylation reaction is always under a mixed ECE-DISP1 kinetic control. The first step of the reaction is an attack, via the oxygen atom, of the electrogenerated ketyl radical anion RR'CO•- at CO2. Further reduction of the carbonate-like adduct arising by such an attack followed by a second carboxylation reaction gives an arene-2-carboxylic acid.

Reductive activation of arenes: XIX. Mechanism and some synthetic applications of the alkylation of phthalodinitrile radical anion

2006 ◽  
Vol 42 (9) ◽  
pp. 1280-1288 ◽  
Author(s):  
E. V. Panteleeva ◽  
T. A. Vaganova ◽  
E. A. Luk’yanets ◽  
V. D. Shteingarts
Keyword(s):  
Radical Anion ◽  
Reductive Activation

scholarly journals N-chlorination mediates protective and immunomodulatory effects of oxidized human plasma proteins

2019 ◽  
Author(s):  
Agnes Ulfig ◽  
Anton V. Schulz ◽  
Alexandra Müller ◽  
Natalie Lupilov ◽  
Lars I. Leichert
Keyword(s):  
Immune Cells ◽  
Plasma Proteins ◽  
Feedback Loop ◽  
Hypochlorous Acid ◽  
Basic Amino Acid ◽  
Immunomodulatory Effects ◽  
Positive Feedback Loop ◽  
Amino Acid Side Chains ◽  
Blood Plasma Proteins ◽  
Reversible Nature

ABSTRACTHypochlorous acid (HOCl), a powerful antimicrobial oxidant, is produced by neutrophils to fight infections. Here we show thatN-chlorination, induced by HOCl concentrations encountered at sites of inflammation, converts blood plasma proteins into chaperone-like holdases that protect other proteins from aggregation. This chaperone-like conversion was reversible by antioxidants and was abrogated by prior methylation of basic amino acids. Furthermore, reversibleN-chlorination of basic amino acid side chains is the major factor that converts plasma proteins into efficient activators of immune cells. Finally, HOCl-modified serum albumin was found to act as a pro-survival molecule that protects neutrophils from cell death induced by highly immunogenic foreign antigens. We propose that activation and enhanced persistence of neutrophils mediated by HOCl-modified plasma proteins, resulting in the increased and prolonged generation of ROS, including HOCl, constitutes a potentially detrimental positive feedback loop that can only be attenuated through the reversible nature of the modification involved.

scholarly journals Biomimetic Ketone Reduction by Disulfide Radical Anion

Molecules ◽  
2021 ◽  
Vol 26 (18) ◽  
pp. 5429
Author(s):  
Sebastian Barata-Vallejo ◽  
Konrad Skotnicki ◽  
Carla Ferreri ◽  
Bronislaw Marciniak ◽  
Krzysztof Bobrowski ◽  
...  
Keyword(s):  
Radical Anion ◽  
Radical Mechanism ◽  
Cyclic Ketones ◽  
High Concentration ◽  
Radical Chain ◽  
Ketyl Radical ◽  
Electron Reduction ◽  
The One ◽  
Key Steps ◽  
Radical Chain Reaction

The conversion of ribonucleosides to 2′-deoxyribonucleosides is catalyzed by ribonucleoside reductase enzymes in nature. One of the key steps in this complex radical mechanism is the reduction of the 3′-ketodeoxynucleotide by a pair of cysteine residues, providing the electrons via a disulfide radical anion (RSSR•−) in the active site of the enzyme. In the present study, the bioinspired conversion of ketones to corresponding alcohols was achieved by the intermediacy of disulfide radical anion of cysteine (CysSSCys)•− in water. High concentration of cysteine and pH 10.6 are necessary for high-yielding reactions. The photoinitiated radical chain reaction includes the one-electron reduction of carbonyl moiety by disulfide radical anion, protonation of the resulting ketyl radical anion by water, and H-atom abstraction from CysSH. The (CysSSCys)•− transient species generated by ionizing radiation in aqueous solutions allowed the measurement of kinetic data with ketones by pulse radiolysis. By measuring the rate of the decay of (CysSSCys)•−at λmax = 420 nm at various concentrations of ketones, we found the rate constants of three cyclic ketones to be in the range of 104–105 M−1s−1 at ~22 °C.

EPR Support for the Ketyl Radical-Anion “Triggered” [3,3]-Sigmatropic Rearrangement

2002 ◽  
Vol 67 (18) ◽  
pp. 6579-6581 ◽  
Author(s):  
Eric J. Enholm ◽  
Merle A. Battiste ◽  
Maria Gallagher ◽  
Kelley M. Moran ◽  
Angelo Alberti ◽  
...  
Keyword(s):  
Radical Anion ◽  
Sigmatropic Rearrangement ◽  
Ketyl Radical

The effect of cycloheximide and cycloheximide analogues on protein, asparagine, and glutamine synthesis in corn root tips

1978 ◽  
Vol 56 (22) ◽  
pp. 2873-2877 ◽  
Author(s):  
W. George Wheatley ◽  
Ann Oaks
Keyword(s):  
Protein Synthesis ◽  
Basic Amino Acid ◽  
Hydroxyl Group ◽  
Root Tips ◽  
Inhibit Protein Synthesis ◽  
Corn Root ◽  
Structural Analogues ◽  
Ketone Carbonyl ◽  
Glutamine Synthesis ◽  
Organic Acids And Sugars

Cycloheximide treatment (3.6 × 10−6 M) inhibits the incorporation of [2-14C]acetate into protein, asparagine, and the organic acids and sugars fraction. At the same time, it enhances the release of 14CO2 and the incorporation of carbon into glutamine and the neutral and basic amino acid fraction. Eight structural analogues of cycloheximide were tested for their effects on protein, asparagine, and glutamine formation in corn root tips. Two analogues, cycloheximide acetate and streptovitacin A (at a concentration of 1.8 × 10−5 M), acted in a manner similar to cycloheximide. Their effect was to inhibit protein and asparagine synthesis and to enhance glutamine formation. Six other analogues (1.8 × 10−5 M) had no marked effect on these fractions. The results of this investigation indicate that the structural analogues which inhibit asparagine formation in corn root tips also inhibit protein synthesis. The results suggest that the hydroxyl group of the hydroxyethylglutarimide portion of the cycloheximide molecule and the ketone-carbonyl group of the cyclohexanone ring are important for their action on protein synthesis in corn root tips.

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