The role of stereoelectronic effects on the side-chain fragmentation of alkylaromatic radical cations. The reactivity of 5-methoxy-2,2-dimethylindan-1-ol radical cation

Tetrahedron ◽  
2002 ◽  
Vol 58 (25) ◽  
pp. 5039-5044 ◽  
Author(s):  
Monica Bellanova ◽  
Massimo Bietti ◽  
Gianfranco Ercolani ◽  
Michela Salamone
Keyword(s):  
Radical Cation ◽  
Radical Cations ◽  
Side Chain ◽  
Stereoelectronic Effects

The role of oxygen acidity on the side-chain fragmentation of ring methoxylated benzocycloalkenol radical cations

2003 ◽  
Vol 44 (34) ◽  
pp. 6401-6404 ◽  
Author(s):  
Monica Bellanova ◽  
Massimo Bietti ◽  
Michela Salamone
Keyword(s):  
Radical Cations ◽  
Side Chain

The role of peroxidases, radical cations and oxygen in the degradation of lignin

1987 ◽  
Vol 321 (1561) ◽  
pp. 495-505 ◽  
Keyword(s):  
Radical Cation ◽  
Active Oxygen Species ◽  
Bond Cleavage ◽  
White Rot Fungi ◽  
Radical Cations ◽  
Veratryl Alcohol ◽  
White Rot ◽  
Oxygen Species ◽  
Lignin Model

Ligninase is an extracellular peroxidase produced by several species of white-rot fungi. It is able to oxidize methoxylated substrates to radical cation intermediates that can undergo C—H or C—C bond cleavage, thereby providing the basis for the oxidation of veratryl alcohol or degradation of lignin model compounds respectively. In some cases, the radical cation intermediate can act as an oxidant, accepting an electron from a suitable donor. It can thus function as a mediator, causing oxidation in a polymer not immediately accessible to the enzyme. This could be important in the degradation of natural lignocellulose substrates. However, the removal of a single electron by a mediator would leave a radical in the polymer. We propose that oxygen will bind to this radical to generate active oxygen species. This provides a potential mechanism for the auto-oxidation of lignin at a distance from the enzyme. A scheme is presented to account for the observation that ligninase can open the ring of veratryl alcohol.

Gas-phase proton-transport self-catalysed isomerisation of glutamine radical cation: The important role of the side-chain

2007 ◽  
Vol 118 (3) ◽  
pp. 589-595 ◽  
Author(s):  
Adrià Gil ◽  
Sílvia Simon ◽  
Mariona Sodupe ◽  
Juan Bertran
Keyword(s):  
Gas Phase ◽  
Radical Cation ◽  
Proton Transport ◽  
Side Chain

Electron n-doping of a highly electron-deficient chlorinated benzodifurandione-based oligophenylene vinylene polymer using benzyl viologen radical cations

2021 ◽  
Author(s):  
Teck Lip Dexter Tam ◽  
Albertus Denny Handoko ◽  
Ting Ting Lin ◽  
Jianwei Xu
Keyword(s):  
Radical Cation ◽  
Radical Cations ◽  
Benzyl Viologen ◽  
Electron Doping ◽  
N Doping ◽  
Polyphenylene Vinylene

Successful electron-doping of highly electron-deficient chlorinated benzodifurandione-based polyphenylene vinylene using viologen radical cation.

scholarly journals “Newton’s cradle” proton relay with amide–imidic acid tautomerization in inverting cellulase visualized by neutron crystallography

2015 ◽  
Vol 1 (7) ◽  
pp. e1500263 ◽  
Author(s):  
Akihiko Nakamura ◽  
Takuya Ishida ◽  
Katsuhiro Kusaka ◽  
Taro Yamada ◽  
Shinya Fushinobu ◽  
...  
Keyword(s):  
Glycoside Hydrolases ◽  
Side Chain ◽  
Enzymatic Reactions ◽  
X Ray Diffraction ◽  
Peptide Bonds ◽  
Proton Relay ◽  
Newton’S Cradle ◽  
Dynamics Simulations ◽  
Hydrolysis Of

Hydrolysis of carbohydrates is a major bioreaction in nature, catalyzed by glycoside hydrolases (GHs). We used neutron diffraction and high-resolution x-ray diffraction analyses to investigate the hydrogen bond network in inverting cellulase PcCel45A, which is an endoglucanase belonging to subfamily C of GH family 45, isolated from the basidiomycete Phanerochaete chrysosporium. Examination of the enzyme and enzyme-ligand structures indicates a key role of multiple tautomerizations of asparagine residues and peptide bonds, which are finally connected to the other catalytic residue via typical side-chain hydrogen bonds, in forming the “Newton’s cradle”–like proton relay pathway of the catalytic cycle. Amide–imidic acid tautomerization of asparagine has not been taken into account in recent molecular dynamics simulations of not only cellulases but also general enzyme catalysis, and it may be necessary to reconsider our interpretation of many enzymatic reactions.

scholarly journals The Role of Arg13 in Protein Phosphatase M tPphA from Thermosynechococcus elongatus

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Jiyong Su ◽  
Karl Forchhammer
Keyword(s):  
Amino Acid ◽  
Protein Phosphatase ◽  
Arginine Residue ◽  
Side Chain ◽  
Wild Type ◽  
Catalytic Center ◽  
Nitrophenyl Phosphate ◽  
Reduced Activity ◽  
Amino Acid Variants

A highly conserved arginine residue is close to the catalytic center of PPM/PP2C-type protein phosphatases. Different crystal structures of PPM/PP2C homologues revealed that the guanidinium side chain of this arginine residue can adopt variable conformations and may bind ligands, suggesting an important role of this residue during catalysis. In this paper, we randomly mutated Arginine 13 of tPphA, a PPM/PP2C-type phosphatase from Thermosynechococcus elongatus, and obtained 18 different amino acid variants. The generated variants were tested towards p-nitrophenyl phosphate and various phosphopeptides. Towards p-nitrophenyl phosphate as substrate, twelve variants showed 3–7 times higher Km values than wild-type tPphA and four variants (R13D, R13F, R13L, and R13W) completely lost activity. Strikingly, these variants were still able to dephosphorylate phosphopeptides, although with strongly reduced activity. The specific inability of some Arg-13 variants to hydrolyze p-nitrophenyl phosphate highlights the importance of additional substrate interactions apart from the substrate phosphate for catalysis. The properties of the R13 variants indicate that this residue assists in substrate binding.

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