A comparison of horseradish peroxidase and manganese ions as catalysts for the oxidation of dihydroxyfumaric acid.
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ABSTRACT:
SUBMITTER: Hartree EF
PROVIDER: S-EPMC1198702 | biostudies-other | 1968 Apr
REPOSITORIES: biostudies-other
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Project description:Lignin peroxidase oxidizes non-phenolic substrates by one electron to give aryl-cation-radical intermediates, which react further to give a variety of products. The present study investigated the possibility that other peroxidative and oxidative enzymes known to catalyse one-electron oxidations may also oxidize non-phenolics to cation-radical intermediates and that this ability is related to the redox potential of the substrate. Lignin peroxidase from the fungus Phanerochaete chrysosporium, horseradish peroxidase (HRP) and laccase from the fungus Trametes versicolor were chosen for investigation with methoxybenzenes as a homologous series of substrates. The twelve methoxybenzene congeners have known half-wave potentials that differ by as much as approximately 1 V. Lignin peroxidase oxidized the ten with the lowest half-wave potentials, whereas HRP oxidized the four lowest and laccase oxidized only 1,2,4,5-tetramethoxybenzene, the lowest. E.s.r. spectroscopy showed that this congener is oxidized to its cation radical by all three enzymes. Oxidation in each case gave the same products: 2,5-dimethoxy-p-benzoquinone and 4,5-dimethoxy-o-benzoquinone, in a 4:1 ratio, plus 2 mol of methanol for each 1 mol of substrate. Using HRP-catalysed oxidation, we showed that the quinone oxygen atoms are derived from water. We conclude that the three enzymes affect their substrates similarly, and that whether an aromatic compound is a substrate depends in large part on its redox potential. Furthermore, oxidized lignin peroxidase is clearly a stronger oxidant than oxidized HRP or laccase. Determination of the enzyme kinetic parameters for the methoxybenzene oxidations demonstrated further differences among the enzymes.
| S-EPMC1131457 | biostudies-other
Project description:Horseradish peroxidase catalyses the oxidation of NAD dimers, (NAD)2, to NAD+ in accordance with a reaction that is pH-dependent and requires 1 mol of O2 per 2 mol of (NAD)2. Horseradish peroxidase also catalyses the peroxidation of (NAD)2 to NAD+. In contrast, bacterial NADH peroxidase does not catalyse the peroxidation or the oxidation of (NAD)2. A free-radical mechanism is proposed for both horseradish-peroxidase-catalysed oxidation and peroxidation of (NAD)2.
| S-EPMC1144724 | biostudies-other
Project description:Horseradish peroxidase (HRP) and laccase are well known oxidases, which have been widely applied for the biosynthesis of organic compounds. In the present work, flavone analogues as an important type of bioactive natural product could be oxidized by HRP or laccase, which afforded dimeric and oxidative flavones. All of the flavone analogues usually possessing phenolic groups could be transformed using HRP. However, only flavonols, isoflavones and chalcones with phenolic groups and dihydroxylflavones were effective substrates of laccase. The radical reaction mechanism with the B-ring of flavone analogues as the radical reaction trigger was proposed for the oxidation of flavones. In silico molecular docking analyses for assaying the interaction between flavone analogues and oxidases indicated that the phenolic groups at the B rings of flavones docked into the HEME active pocket of HRP well. Kinetic behaviors of the oxidation for various flavone analogues mediated by HRP or laccase displayed Hill and substrate inhibition kinetic models. Therefore, in the present work, the oxidation of various flavone analogues mediated by HRP or laccase has been successfully characterized, which would be helpful for the preparation of flavone derivatives.
| S-EPMC9063861 | biostudies-literature
Project description:Incorporation of Mn into an established water oxidation catalyst based on a Co(III)4O4 cubane was achieved by a simple and efficient assembly of permanganate, cobalt(II) acetate, and pyridine to form the cubane oxo cluster MnCo3O4(OAc)5py3 (OAc = acetate, py = pyridine) (1-OAc) in good yield. This allows characterization of electronic and chemical properties for a manganese center in a cobalt oxide environment, and provides a molecular model for Mn-doped cobalt oxides. The electronic properties of the cubane are readily tuned by exchange of the OAc- ligand for Cl- (1-Cl), NO3- (1-NO3), and pyridine ([1-py]+). EPR spectroscopy, SQUID magnetometry, and DFT calculations thoroughly characterized the valence assignment of the cubane as [MnIVCoIII3]. These cubanes are redox-active, and calculations reveal that the Co ions behave as the reservoir for electrons, but their redox potentials are tuned by the choice of ligand at Mn. This MnCo3O4 cubane system represents a new class of easily prepared, versatile, and redox-active oxido clusters that should contribute to an understanding of mixed-metal, Mn-containing oxides.
| S-EPMC5553203 | biostudies-literature
Project description:Horseradish peroxidase C (HRPC) binds 2 mol calcium per mol of enzyme with binding sites located distal and proximal to the heme group. The effect of calcium depletion on the conformation of the heme was investigated by combining polarized resonance Raman dispersion spectroscopy with normal coordinate structural decomposition analysis of the hemes extracted from models of Ca(2+)-bound and Ca(2+)-depleted HRPC generated and equilibrated using molecular dynamics simulations. Results show that calcium removal causes reorientation of heme pocket residues. We propose that these rearrangements significantly affect both the in-plane and out-of-plane deformations of the heme. Analysis of the experimental depolarization ratios are clearly consistent with increased B(1g)- and B(2g)-type distortions in the Ca(2+)-depleted species while the normal coordinate structural decomposition results are indicative of increased planarity for the heme of Ca(2+)-depleted HRPC and of significant changes in the relative contributions of three of the six lowest frequency deformations. Most noteworthy is the decrease of the strong saddling deformation that is typical of all peroxidases, and an increase in ruffling. Our results confirm previous work proposing that calcium is required to maintain the structural integrity of the heme in that we show that the preferred geometry for catalysis is lost upon calcium depletion.
| S-EPMC1302820 | biostudies-literature
Project description:BACKGROUND: Horseradish peroxidases (HRPs) from Armoracia rusticana have long been utilized as reporters in various diagnostic assays and histochemical stainings. Regardless of their increasing importance in the field of life sciences and suggested uses in medical applications, chemical synthesis and other industrial applications, the HRP isoenzymes, their substrate specificities and enzymatic properties are poorly characterized. Due to lacking sequence information of natural isoenzymes and the low levels of HRP expression in heterologous hosts, commercially available HRP is still extracted as a mixture of isoenzymes from the roots of A. rusticana. RESULTS: In this study, a normalized, size-selected A. rusticana transcriptome library was sequenced using 454 Titanium technology. The resulting reads were assembled into 14871 isotigs with an average length of 1133 bp. Sequence databases, ORF finding and ORF characterization were utilized to identify peroxidase genes from the 14871 isotigs generated by de novo assembly. The sequences were manually reviewed and verified with Sanger sequencing of PCR amplified genomic fragments, resulting in the discovery of 28 secretory peroxidases, 23 of them previously unknown. A total of 22 isoenzymes including allelic variants were successfully expressed in Pichia pastoris and showed peroxidase activity with at least one of the substrates tested, thus enabling their development into commercial pure isoenzymes. CONCLUSIONS: This study demonstrates that transcriptome sequencing combined with sequence motif search is a powerful concept for the discovery and quick supply of new enzymes and isoenzymes from any plant or other eukaryotic organisms. Identification and manual verification of the sequences of 28 HRP isoenzymes do not only contribute a set of peroxidases for industrial, biological and biomedical applications, but also provide valuable information on the reliability of the approach in identifying and characterizing a large group of isoenzymes.
| S-EPMC3987668 | biostudies-literature
Project description:EDTA inhibits horseradish peroxidase (HRP)-catalysed iodide oxidation in a concentration and pH-dependent manner. It is more effective at pH 6 than at lower pH values. A plot of log Kiapp. values as a function of pH yields a sigmoidal curve from which a pKa value of 5.4 can be calculated for an ionizable group on the catalytically active HRP for EDTA inhibition. Among the structural analogues of EDTA, tetramethylethylenediamine (TEMED) is 80% as effective as EDTA, whereas the EDTA-Zn2+ chelate and EGTA are ineffective. Kinetic studies indicate that EDTA competitively inhibits iodide oxidation. Spectral studies show that EDTA can quickly reduce compound I to compound II, but reduction of preformed compound II to the native enzyme is relatively slow, as demonstrated by the time-dependent spectral shift from 417 nm to 402 nm through an isosbestic point at 408 nm. Under steady-state conditions, in a reaction mixture containing HRP, EDTA and H2O2, the enzyme remains in the compound-II form, with absorption maxima at 417, 527 and 556 nm. Direct evidence for one-electron oxidation of EDTA by HRP intermediates is provided by the appearance of an e.s.r. signal of a 5,5-dimethyl-1-pyrroline N-oxide (spin trap)-EDTA radical adduct [aN (hyperfine splitting constant) = 1.5 mT] in e.s.r. studies. The signal intensity, however, decreases in the presence of iodide. The KD of the HRP-EDTA complex obtained from optical difference spectroscopy increases with an increase in iodide concentration, and the double-reciprocal plot for EDTA binding indicates that EDTA and iodide compete for the same binding site for oxidation. We suggest that EDTA inhibits iodide oxidation by acting as an electron donor.
| S-EPMC1137937 | biostudies-other
Project description:Manganese(II) complex [(Bn-tpen)MnII]2+ activated dioxygen for oxidation of cyclohexene in acetonitrile (MeCN) and methanol (MeOH). In MeCN, ketone (2-cyclohexen-1-one), alcohol (2-cyclohexen-1-ol) and small amounts of epoxide (cyclohexene oxide) were produced in this reaction, while in MeOH only ketone was formed. In the most efficient experiment, the combination of 2.5 × 10-4 mol% [(Bn-tpen)MnII]2+ and 4 M cyclohexene under dioxygen atmosphere (pO2 = 1 atm) in MeCN after 24 h of reaction, gave the TON equal to 716, and the main oxidation products were ketone (196 mM) and alcohol (147 mM), whereas epoxide was formed in insignificant amounts (15 mM). The formation of [(Bn-tpen)MnIV=O]2+ and [(Bn-tpen)MnIII-OH]2+ species was confirmed. The novelty of this work is the observation, that in both solvents, [(Bn-tpen)MnII]2+ complex is initially oxidized by t-BuOOH to produce Mn(III)-complex, which is reduced back by cyclohexene to [(Bn-tpen)MnII]2+, and the latter species is an active catalyst of c-C6H10 oxidation. Knowledge of the electrochemical properties of the system components may contribute to understanding the mechanisms involving participation of the active agents created in the system.
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Project description:Cryptomelane is an abundant mineral manganese oxide with unique physicochemical features. This work investigates the real capabilities of cryptomelane as an oxidation catalyst. In particular, the preferential CO oxidation (CO-PROX), has been studied as a simple reaction model. When doped with copper, the cryptomelane-based material has revealed a great potential, displaying a comparable activity to the high-performance CuO/CeO2. Despite stability concerns that compromise the primary catalyst reusability, CuO/cryptomelane is particularly robust in the presence of CO2 and H2O, typical components of realistic CO-PROX streams. The CO-PROX reaction mechanism has been assessed by means of isotopic oxygen pulse experiments. Altogether, CuO/CeO2 shows a greater oxygen lability, which facilitates lattice oxygen enrolment in the CO-PROX mechanism. In the case of CuO/cryptomelane, in spite of its lower oxygen mobility, the intrinsic structural water co-assists as active oxygen species involved in CO-PROX. Thus, the presence of moisture in the reaction stream turns out to be beneficial for the stability of the cryptomelane structure, besides aiding into the active oxygen restitution in the catalyst. Overall, this study proves that CuO/cryptomelane is a promising competitor to CuO/CeO2 in CO-PROX technology, whose implementation can bring the CO-PROX technology and H2 purification processes a more sustainable nature.
| S-EPMC8461565 | biostudies-literature
Project description:Hydrogels provide promising applications in tissue engineering and regenerative medicine, with silk fibroin (SF) offering biocompatibility, biodegradability and tunable mechanical properties. The molecular weight (MW) distribution of SF chains varies from ∼80 to 400 kDa depending on the extraction and purification process utilized to prepare the protein polymer. Here, we report a fundamental study on the effect of different silk degumming (extraction) time (DT) on biomaterial properties of enzymatically crosslinked hydrogels, including secondary structure, mechanical stiffness, in vitro degradation, swelling/contraction, optical transparency and cell behaviour. The results indicate that DT plays a crucial role in determining material properties of the hydrogel; decrease in DT increases β-sheet (crystal) formation and mechanical stiffness while decreasing degradation rate and optical transparency. The findings on the relationships between properties of silk hydrogels and DT should facilitate the more rational design of silk-based hydrogel biomaterials to match properties needed for diverse purpose in biomedical engineering.
| S-EPMC7390697 | biostudies-literature