scholarly journals The involvement of the bridging imidazolate in the catalytic mechanism of action of bovine superoxide dismutase

1977 ◽  
Vol 167 (1) ◽  
pp. 271-274 ◽  
Author(s):  
M E McAdam ◽  
E M Feilden ◽  
F Lavelle ◽  
L Calabrese ◽  
D Cocco ◽  
...  
Keyword(s):  
Superoxide Dismutase ◽  
Nitrogen Atom ◽  
Mechanism Of Action ◽  
Pulse Radiolysis ◽  
Catalytic Mechanism ◽  
Catalytic Reduction ◽  
Rapid Change ◽  
Proton Donor ◽  
Spectral Changes ◽  
Rapid Protonation

The pulse-radiolysis method has been used to study the catalytic mechanism of O2 leads to dismutation by the Co(II)-substituted bovine erythrocuprein (superoxide dismutase, EC 1.15.1.1). Catalysis is accompanied by spectral changes that may be interpreted in terms of rapid protonation and deprotonation of the Cu-facing nitrogen atom of the imidazolate that bridges the Cu(II) and the Co(II) [or Zn(II)] in the oxidized enzyme. This rapid change permits the possibility that the imidazole is a proton donor in the catalytic reduction of O2 leads to.

scholarly journals A pulse-radiolysis study of the catalytic mechanism of the iron-containing superoxide dismutase from Photobacterium leiognathi

1977 ◽  
Vol 161 (1) ◽  
pp. 3-11 ◽  
Author(s):  
F Lavelle ◽  
M E McAdam ◽  
E M Fielden ◽  
P B Roberts ◽  
K Puget ◽  
...  
Keyword(s):  
Superoxide Dismutase ◽  
Rate Constant ◽  
Pulse Radiolysis ◽  
Ferric Iron ◽  
Catalytic Mechanism ◽  
Order Rate Constant ◽  
Sodium Ascorbate ◽  
Paramagnetic Resonance ◽  
Photobacterium Leiognathi ◽  
Ph Range

The mechanism of the enzymic reaction of an iron-containing superoxide dismutase purified from the marine bacterium Photobacterium leiognathi was studied by using pulse radiolysis. Measurements of activity were done with two different preparations of enzyme containing either 1.6 or 1.15 g-atom of iron/mol. In both cases, identical values of the second-order rate constant for reaction between superoxide dismutase and the superoxide ion in the pH range 6.2-9.0 (k=5.5 X 10(8) M-1-S-1 at pH 8.0) were found. As with the bovine erythrocuprein, there was no evidence for substrate saturation. The effects of reducing agents (H2O2, sodium ascorbate or CO2 radicals) on the visible and the electron-paramagnetic-resonance spectra of the superoxide dismutase containing 1.6 g-atom of ferric iron/mol indicate that this enzyme contains two different types of iron. Turnover experiments demonstrate that only that fraction of the ferric iron that is reduced by H2O2 is involved in the catalysis, being alternately oxidized and reduced by O2; both the oxidation and the reduction steps have a rate constant equal to that measured under turnover conditions. These results are interpreted by assuming that the superoxide dismutase isolated from the organism contains 1 g-atom of catalytic iron/mol and a variable amount of non-catalytic iron. This interpretation is discused in relation to the stoicheiometry reported for iron-containing superoxide dismutases prepared from several other organisms.

The structure and mechanism of action of papain

1970 ◽  
Vol 257 (813) ◽  
pp. 237-248 ◽  
Keyword(s):  
Mechanism Of Action ◽  
Catalytic Mechanism ◽  
Proteolytic Enzymes ◽  
Cysteine Proteinase ◽  
Preceding Paper ◽  
Cysteine Residue ◽  
Enzymic Activity ◽  
Critical Survey ◽  
Cysteine Proteinases ◽  
Stem Bromelain

The cysteine proteinases form a group of enzymes which depend for their enzymic activity on the thiol group of a cysteine residue. Several which occur in plants have been investigated extensively and include papain, ficin and stem bromelain (Smith & Kimmel i960). Although the term papain, introduced last century to describe the proteolytic principle in papaya latex (Wurtz & Bouchut 1879) is still used to describe crude dried latex, the crystalline enzyme is readily obtained (Kimmel & Smith 1954). Ficin is known to consist of several closely related enzymes which have been resolved (Sgarbieri, Gupte, Kramer & Whitaker 1964), but for most structural and mechanistic studies the unresolved mixture of enzymes has been used. Stem bromelain also appears to be a mixture of at least two proteolytic enzymes which have not yet been resolved (Ota, Moore & Stein 1962; Murachi 1964). In spite of the recognized heterogeneity of ficin and stem bromelain, it does seem that both structurally and mechanistically they are similar to papain. Only one bacterial cysteine proteinase has received a detailed study, namely, streptococcal proteinase, and it appears to have little or no relation in its amino acid sequence with the plant enzymes (Liu, Stein, Moore & Elliott 1965). The functional groups involved in the catalytic mechanism are apparently the same as in the plant proteinases (Gerwin, Stein & Moore 1966; Liu 1967; Husain & Lowe 1968 a , c ), but the mechanism of action has not been extensively studied. It may well be however that the plant and bacterial cysteine proteinases have converged onto a similar mechanism of action by two independent evolutionary pathways, as now seems apparent for the animal and bacterial serine proteinases (Alden, Wright & Kraut, this volume, p. 119). Because the tertiary crystal structure of papain (Drenth, Jansonius, Koekoek, Swen & Wolthers 1968; see also the preceding paper, p. 231) is now known, a critical survey of this enzyme is apposite.

scholarly journals Synthesis, Structure, and Properties of a Dinuclear Cu(II) Coordination Polymer Based on Quinoxaline and 3,3-Thiodipropionic Acid Ligands

2021 ◽  
Author(s):  
Adedibu Clement Tella ◽  
Samson Owalude ◽  
Vincent Adimula ◽  
Adetola Oladipo ◽  
Victoria Olayemi ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Nitrogen Atom ◽  
Coordination Polymer ◽  
Elemental Analysis ◽  
Catalytic Reduction ◽  
Copper Acetate ◽  
Structure And Properties ◽  
X Ray Diffraction ◽  
X Ray ◽  
H Nmr

Abstract The coordination polymer [Cu2(TDPH)4(QNX)].DMF, (QNX = Quinoxaline; TDPH = 3,3-thiodipropionic acid), has been prepared by reaction of copper acetate, TDPH, and quinoxaline. The compound was characterized by elemental analysis, FTIR spectroscopy, and single-crystal X-ray diffraction. The crystal is monoclinic with a P21/n space group and dimensions of a = 12.889(3) Å, b = 14.983(4) Å, c = 14.091(3) Å, α = 90 °, β = 90.200(11) °, γ = 90 °, V = 2721.18 (2) Å3, Z = 4. The ligands are hexagonally coordinated to the Cu(II) centre in the form of Cu2O4N with one nitrogen atom from the quinoxaline ligand, and four oxygen atoms from four TDPH molecules in a monodentate fashion. The Cu-Cu bond length was 2.642(1) and 2.629(1) Å for the Cu1----Cu1 and Cu2----Cu2 bonds. The QNX ligand bridged the two copper atoms. The catalytic reduction of 4-nitrophenol to 4-aminophenol using NaBH4 in the presence of [Cu2(TDPH)4(QNX)].DMF, as catalyst was completed within 11 minutes. The 4-aminophenol product was confirmed using 1H NMR spectroscopy.

Reaction mechanism and chemical kinetics of NH3-NO/NO2-SCR system with vanadium-based catalyst under marine diesel exhaust conditions

2019 ◽  
Vol 234 (3) ◽  
pp. 342-352
Author(s):  
Zhanguang Wang ◽  
Yuanqing Zhu ◽  
Song Zhou ◽  
Yongming Feng
Keyword(s):  
Catalytic Mechanism ◽  
Catalytic Reduction ◽  
Reaction Pathway ◽  
Reaction Model ◽  
Temperature Oxidation ◽  
Marine Diesel ◽  
Standard Scr ◽  
Experimental Values ◽  
Scr System ◽  
Kinetics Of

As one of the most effective NOx emission removing technologies to meet the Tier III limitation by International Maritime Organization, urea-selective catalytic reduction (SCR) technology is starting to be used in two-stroke marine diesel engines. Based on the two-cycle catalytic mechanism proposed by Topsoe, in combination with the exhaust characteristics of the marine diesel, expansion studies on detailed SCR reaction model were carried out in this paper. According to the temperature dependence of reaction pathway, SCR reaction model was divided into three parts: low temperature reaction pathway, standard SCR reaction pathway, and high temperature oxidation pathways, and an expanded NH3-NO/NO2-SCR reaction model for V2O5 catalyst was proposed in the paper. In order to verify the accuracy of the expanded SCR reaction model, simulating and testing studies of SCR reaction under marine diesel conditions were carried out with a commercial extruded V2O5/TiO2 catalyst. The simulation values are agreed well with experimental values at 150–500 ℃, and kinetics characteristics of SCR reaction process under V2O5/TiO2 catalyst can be predicted accurately with the expanded NH3-NO/NO2-SCR reaction model.

A pulse radiolysis study of superoxide dismutase

1972 ◽  
Vol 268 (2) ◽  
pp. 605-609 ◽  
Author(s):  
Guiseppe Rotilio ◽  
Robert C Bray ◽  
E.Martin Fielden
Keyword(s):  
Superoxide Dismutase ◽  
Pulse Radiolysis

Effect of substituents at the proton-donor nitrogen atom on an intramolecular hydrogen bond of type NH...O

1974 ◽  
Vol 15 (3) ◽  
pp. 353-356
Author(s):  
L. N. Kurkovaskaya ◽  
I. L. Radushnova ◽  
N. N. Shapet'ko ◽  
S. M. Kvitko ◽  
Yu. S. Andreichikov ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Nitrogen Atom ◽  
Intramolecular Hydrogen Bond ◽  
Proton Donor ◽  
Effect Of Substituents ◽  
Donor Nitrogen Atom ◽  
Donor Nitrogen ◽  
Intramolecular Hydrogen

scholarly journals Evidence for catalytic dismutation of superoxide by cobalt(II) derivatives of bovine superoxide dismutase in aqueous solution as studied by pulse radiolysis

1982 ◽  
Vol 205 (1) ◽  
pp. 181-187 ◽  
Author(s):  
P O'Neill ◽  
E M Fielden ◽  
D Cocco ◽  
G Rotilio ◽  
L Calabrese
Keyword(s):  
Aqueous Solution ◽  
Superoxide Dismutase ◽  
Rate Constants ◽  
Redox Reactions ◽  
Pulse Radiolysis ◽  
Turnover Rate ◽  
Copper Site ◽  
Initial Interaction ◽  
Derivatives Of ◽  
Reaction Schemes

By using the technique of pulse radiolysis to generate O2-., it is demonstrated that Co(II) derivatives of bovine superoxide dismutase in which the copper alone and both the copper and zinc of the enzyme have been substituted by Co(II), resulting in (Co, Zn)- and (Co, Co)-proteins, are capable of catalytically dismutating O2-. with ‘turnover’ rate constants of 4.8×10(6) dm3.s-1.mol-1 and 3.1×10(6) dm3.s-1.mol-1 respectively. The activities of the proteins are independent of the pH (7.4-9.4) and are about three orders of magnitude less than that of the native (Cu, Zn)-protein. The rate constants for the initial interaction of O2-. with the Co-proteins were determined to be (1.5-1.6) X 10(9) dm3.s-1.mol-1; however, in the presence of phosphate, partial inhibition is apparent [k approximately (1.9-2.3) X 10(8) dm3.s-1.mol-1]. To account for the experimental observations, two reaction schemes are presented, involving initially either complex-formation or redox reactions between O2-. and Co(II). This is the first demonstration that substitution of a metal into the vacant copper site of (Cu, Zn)-protein results in proteins that retain superoxide dismutase activity.

pH-Dependent activity and spectral changes in metal-tolerant Fe/Mn-superoxide dismutase

1995 ◽  
Vol 59 (2-3) ◽  
pp. 378
Author(s):  
Fumiyuki Yamakura ◽  
Kazuo Kobayashi ◽  
Daijiro Ohmori ◽  
Yukihiro Hiraoka ◽  
Koji Nakayama
Keyword(s):  
Superoxide Dismutase ◽  
Spectral Changes ◽  
Dependent Activity ◽  
Ph Dependent
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