1,720,985 research outputs found
Potential applications of peroxidases in the fine chemical industries
No full textA description of selected types of reactions catalyzed by heme peroxidases is given. In particular, the discussion is focused mainly on those of potential interest for fine chemical synthesis. The division into subsections has been done from the point of view of the enzyme action, i.e., giving emphasis to themechanism of the enzymatic reaction, and from that of the substrate, i.e., analyzing the type of transformation promoted by the enzyme. These two approaches have several points in common
Myoglobin modification by enzyme-generated dopamine reactive species
No full textThe generation of reactive quinone species (DAQ) from oxidation of dopamine (DA) is involved in neurodegenerative pathologies like Parkinson’s disease (A. Borta, G. U. Höglinger, J. Neurochem. 100, 587-595 (2007)). The oxidation of DA to DAQ can occur either in a single two-electron process or in two consecutive one-electron steps, through semiquinone radicals, giving rise to different pattern of reactions. The former type of reaction can be promoted by tyrosinase, the latter by peroxidases in the presence of H2O2, which can be formed under oxidative stress conditions. Both enzymes were employed for the characterization of the thiol-catechol adducts formed by reaction of DA and cysteine or glutathione, and for the identification of specific amino acid residues modified by DAQs in two representative target proteins, human and horse heart myoglobin.
Our results indicate that the cysteinyl-DA adducts are formed from the same quinone intermediate independently of the mechanism of DA oxidation, and that the hallmark of a radical mechanism is the formation of the cystine dimer. The reactivity of quinone species also controls the DA promoted derivatization of histidine residues in proteins. However, for the modification of the cysteine residue in human myoglobin, a radical intramolecular mechanism has been proposed, in which the protein acts both as the catalyst and target of the reaction. Most importantly, the modification of myoglobins through DAQ linkages, and in particular by DA oligomers, has dramatic effects on their stability, as it induces protein unfolding and incorporation into insoluble melanic precipitates
A Cu-bis(imidazole) Substrate Intermediate Is the Catalytically Competent Center for Catechol Oxidase Activity of Copper Amyloid-β
No full textInteraction of copper ions with Aβ peptides alters the redox activity of the metal ion and can be associated with neurodegeneration. Many studies deal with the characterization of the copper binding mode responsible for the reactivity. Oxidation experiments of dopamine and related catechols by copper(II) complexes with the N-terminal amyloid-β peptides Aβ16 and Aβ9, and the Aβ16[H6A] and Aβ16[H13A] mutant forms, both in their free amine and N-acetylated forms show that efficient reactivity requires the oxygenation of a CuI-bis(imidazole) complex with a bound substrate. Therefore, the active intermediate for catechol oxidation differs from the proposed "in-between state" for the catalytic oxidation of ascorbate. During the catechol oxidation process, hydrogen peroxide and superoxide anion are formed but give only a minor contribution to the reaction
Catalytic Activity of Myoglobin Immobilized on Zirconium Phosphonates.
Full text linkThe adsorption and catalytic activity of myoglobin (Mb) on zirconium phosphonates (R-zirconium
benzenephosphonate (R-ZrBP), R-zirconium carboxyethanephosphonate (R-ZrCEP), and a novel layered
zirconium fluoride aminooctyl-N,N-bis(methylphosphonate) (ZrC8)) were investigated. The maximum
adsorption was reached after 16 h of contact and was greater on hydrophobic supports such as R-ZrBP
and ZrC8 compared to hydrophilic supports such as R-ZrCEP. The equilibrium adsorption isotherms fitted
the Langmuir equation, suggesting the presence of a monolayer of protein molecules on the support surfaces.
The catalytic activities of free Mb and of the obtained biocomposites were studied in terms of the oxidation
of two aromatic substrates, o-phenylenediamine and 2-methoxyphenol (guaiacol), by hydrogen peroxide.
The oxidation catalyzed by immobilized myoglobin followed the Michaelis-Menten kinetics, similar to
oxidation by free Mb. The kinetic parameters, kcat and KM, were significantly affected by the adsorption
process. Mb/R-ZrCEP was the most efficient biocatalyst obtained, probably because of the hydrophilic
nature of the support. The effect of immobilization on the stability of Mb toward inactivation by hydrogen
peroxide was also investigated, and an increased resistance was found. The biocomposites obtained can
be stored at 4 °C for months without a significant loss of catalytic activity
Peroxidase catalyzed nitration of tryptophan derivatives. Mechanism, products and comparison with chemical nitrating agents
No full textNitrite increases the enantioselectivity of sulfoxidation catalyzed by myoglobin derivatives in the presence of hydrogen peroxide
No full textMetMyoglobin-Catalyzed Exogenous and Endogenous Tyrosine Nitration by Nitrite and Hydrogen Peroxide
No full textMetmyoglobin catalyzes the nitration of various phenolic compounds in the presence of nitrite and hydrogen peroxide. The reaction rate depends on the reactant concentrations showing saturation behavior. Two competing paths are responsible for the reaction. In the first one, myoglobin reacts according to a peroxidase-like cycle forming two active intermediates, which can induce one-electron oxidation of the substrates. The MbFeIV=O intermediate oxidizes nitrite to nitrogen dioxide which, after reaction with the phenol or with a phenoxy radical, yields the nitrophenol. In the second mechanism, hydrogen peroxide reacts with the iron-bound nitrite to produce an active nitrating species, which we assume to be a protein bound peroxynitrite species, MbFeIII-N(O)OO. The high nitrating power of the active species is shown by the fact that the catalytic rate constant is essentially independent on the redox properties of the phenol. The occurrence of one or other of these mechanisms depends on the nitrite concentration: at low [NO2-] the nitrating agent is nitrogen dioxide, whereas at high [NO2-] the peroxynitrite path is dominant. The myoglobin derivative that accumulates during turnover depends on the mechanism. When the path involving NO2• is dominant, the spectrum of the MbFeIV=O intermediate is observed. At high nitrite concentration, the Soret band appears at 416 nm, which we attribute to an iron-peroxynitrite species. The metMb/NO2-/H2O2 system competitively nitrates the heme and the endogenous tyrosine at position 146 of the protein. Phenolic substrates protect Tyr146 from nitration by scavenging the active nitrating species. The exposed Tyr103 residue is not nitrated under the same conditions
Engineering and Prosthetic-Group Modification of Myoglobin: Peroxidase Activity, Chemical Stability and Unfolding Properties
No full textOxidase Reactivity of CuII Bound to N-Truncated Aβ Peptides Promoted by Dopamine
No full textThe redox chemistry of copper(II) is strongly modulated by the coordination to amyloid-β peptides and by the stability of the resulting complexes. Amino-terminal copper and nickel binding motifs (ATCUN) identified in truncated Aβ sequences starting with Phe4 show very high affinity for copper(II) ions. Herein, we study the oxidase activity of [Cu–Aβ4−x] and [Cu–Aβ1−x] complexes toward dopamine and other catechols. The results show that the CuII–ATCUN site is not redox-inert; the reduction of the metal is induced by coordination of catechol to the metal and occurs through an inner sphere reaction. The generation of a ternary [CuII–Aβ–catechol] species determines the efficiency of the oxidation, although the reaction rate is ruled by reoxidation of the CuI complex. In addition to the N-terminal coordination site, the two vicinal histidines, His13 and His14, provide a second Cu-binding motif. Catechol oxidation studies together with structural insight from the mixed dinuclear complexes Ni/Cu–Aβ4−x reveal that the His-tandem is able to bind CuII ions independently of the ATCUN site, but the N-terminal metal complexation reduces the conformational mobility of the peptide chain, preventing the binding and oxidative reactivity toward catechol of CuII bound to the secondary site
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