Peroxidase oxidation reaction

The existence of chaotic oscillations has been documented in a variety of chemical systems. Some of tire earliest observations of chemical chaos have been on biochemical systems like tire peroxidase-oxidase reaction [12] and on tire well known Belousov-Zhabotinskii (BZ) [13] reaction. The BZ reaction is tire Ce-ion-catalyzed oxidation of citric or malonic acid by bromate ion. Early investigations of the BZ reaction used tire teclmiques of dynamical systems tlieory outlined above to document tire existence of chaos in tliis reaction. Apparent chaos in tire BZ reaction was found by Hudson et a] [14] aiid tire data were analysed by Tomita and Tsuda [15] using a return-map metliod. Chaos was confinned in tire BZ reaction carried out in a CSTR by Roux et a] [16, E7] and by Hudson and... 

Detecting the presence of small, even invisible, amounts of blood is routine. Physical characteristics of dried stains give minimal information, however, as dried blood can take on many hues. Many of the chemical tests for the presence of blood rely on the catalytic peroxidase activity of heme (56,57). Minute quantities of blood catalyze oxidation reactions between colorless materials, eg, phenolphthalein, luco malachite green, luminol, etc, to colored or luminescent ones. The oxidant is typically hydrogen peroxide or sodium perborate (see Automated instrumentation,hematology). 

The enzymatic reactions of peroxidases and oxygenases involve a two-electron oxidation of iron(III) and the formation of highly reactive [Fe O] " species with a formal oxidation state of +V. Direct (spectroscopic) evidence of the formation of a genuine iron(V) compound is elusive because of the short life times of the reactive intermediates [173, 174]. These species have been safely inferred from enzymatic considerations as the active oxidants for several oxidation reactions catalyzed by nonheme iron centers with innocent, that is, redox-inactive, ligands [175]. This conclusion is different from those known for heme peroxidases and oxygenases... 

Takahama, U. Oniki T. Shimokawa H. A possible mechanism for the oxidation of sinapyl alcohol hy peroxidase-dependent reactions in the apoplast enhancement of the oxidation hy hydroxycinnamic acids and components of the apoplast. Plant Cell Physiol. 1996, 37, 499-504. 

Takahama, U. Oxidation of hydroxycinnamic acid and hydroxycinnamyl alcohol derivatives by laccase and peroxidase—interactions among p-hydroxyphenyl, guaiacyl and syringyl groups during the oxidation reactions. Physiol. Plantarum 1995, 93, 61-68. 

For oxalate detection, authors proposed a similar detection approach for recognition of oxalate via an immobilized oxalate oxidase/peroxidase couple and dye precursors MBTH (3-methyl-2-benzothiazolinone hydrazone) and DMAB (3-dimethylaminobenzoic acid). The peroxide generated by oxidation of oxalate to CO2 reacted with the dye precursors in a peroxidase-catalyzed reaction to yield an indamine dye with absorption maximum at 590 nm. The concentration of oxalate was correlated with increased absoiption from dye. 

Support for this conclusion is provided by the hydroperoxide specificity of BP oxidation. The scheme presented in Figure 6 requires that the same oxidizing agent is generated by reaction of h2°2/ peroxy acids, or alkyl hydroperoxides with the peroxidase. Oxidation of any compound by the iron-oxo intermediates should be supported by any hydroperoxide that is reduced by the peroxidase. This is clearly not the case for oxidation of BP by ram seminal vesicle microsomes as the data in Figure 7 illustrate. Quinone formation is supported by fatty acid hydroperoxides but very poorly or not at all by simple alkyl hydroperoxides or H2C>2. The fact that... 

Alternative metabolic pathways involve ring-oxidation and peroxidation of arylamines. Although ring-oxidation is generally considered a detoxification reaction, an electrophilic iminoquinone (X) can be formed by a secondary oxidation of the aminophenol metabolite (18,19). Lastly, reactive imines (XI) can be formed from the primary arylamines by peroxidase-catalyzed reactions that involve free radical intermediates (reviewed in 20). 

In this system, choline formed by acetylcholinesterase is oxidized by choline oxidase and the hydrogen peroxide produced is determined using the luminol/peroxidase CL reaction. The sensor has been used for the analysis of Paraoxon and Aldicarb pesticides, with detection limits of 0.75 pg/L and 4 pg/ L, respectively. Recoveries in the range of 81-108% in contaminated samples of soils and vegetables were obtained. 

He got a Habilitation a diriger les recherches in 2008 and he is now developing his own project that consists of the elaboration of new hybrid metalloprotein catalysts for selective oxidation reactions, by insertion of metal cofactors into xylanases. He then studies their peroxidase, catalase, and monooxygenase activities, in particular in the selective oxidation of sulfides, alkanes, and alkenes. 

The heme peroxidases oxidize a variety of structurally diverse substrates by using hydrogen peroxide or hydroperoxides as oxidants, whereby the oxidants are reduced to water or alcohol. In the following, the present state of such peroxidase-catalyzed reactions in organic synthesis is described, which unquestionably is important for preparative work. 

Oxidation of organic contaminants by microorganisms is one of the basic metabolic reactions in the subsurface and involves the presence of a group of oxidative enzymes such as peroxidases, lactases, and mixed-function oxidizes. Major oxidative reactions that may occur in the subsurface are presented and explained in Table 15.2. 

The best known and most nsefnl of the chemiluminescent reactions involving electron transfer is the oxidation of luminol (3.100) or its derivatives in alkaline medium. The oxidant can be hydrogen peroxide, sodium ferricyanide or hypochlorite, usually with a catalyst that can be a transition metal ion, such as Cu " Co +, Fe + and Mtf+, or haem and haemproteins, e.g. peroxidases. The reaction mode is shown in Figure 3.22.4"... 

The oxidation reactions of luminol and lucigenin can be used to assay for H Oj. For example, analysis of glucose in biological systems can be achieved using a three-enzyme system of mutarotase, glucose oxidase and horseradish peroxidase by correlation with the amount of HjOj released. Similarly, cholesterol can be measured using cholesterol oxidase. The fact that the rate of luminol oxidation depends on the concentration of the catalyst can be used as a method for determination of Co +, Fe +, Cr + and Mn + and other catalysts.Some examples of the use of luminol, isolumi-nol and their derivatives in immunoassays are shown in Table 3.11. ... 

Thionamide drugs interfere with peroxidase-catalyzed reactions. In the thyroid gland, they inhibit the activity of the enzyme TPO, which is required for the intrathyroidal oxidation of I , the incorporation of I into Tg, and the coupling of iodotyrosyl residues to form thyroid hormones. Thus, these drugs inhibit thyroid hormone synthesis and with time, also secretion. Propylthiouracil, but not methimazole, also inhibits Dl, which deiodinates T4 to Tj. Because of this additional action, propylthiouracil is often used to provide a rapid alleviation of severe thyrotoxicosis. 

A typical chemical system is the oxidative decarboxylation of malonic acid catalyzed by cerium ions and bromine, the so-called Zhabotinsky reaction this reaction in a given domain leads to the evolution of sustained oscillations and chemical waves. Furthermore, these states have been observed in a number of enzyme systems. The simplest case is the reaction catalyzed by the enzyme peroxidase. The reaction kinetics display either steady states, bistability, or oscillations. A more complex system is the ubiquitous process of glycolysis catalyzed by a sequence of coordinated enzyme reactions. In a given domain the process readily exhibits continuous oscillations of chemical concentrations and fluxes, which can be recorded by spectroscopic and electrometric techniques. The source of the periodicity is the enzyme phosphofructokinase, which catalyzes the phosphorylation of fructose-6-phosphate by ATP, resulting in the formation of fructose-1,6 biphosphate and ADP. The overall activity of the octameric enzyme is described by an allosteric model with fructose-6-phosphate, ATP, and AMP as controlling ligands. 

A comparison of peroxidase and cytochrome P-450 illustrates the problems of comparing enzymes and their related catalysts such as synzymes. Peroxidase has low substrate specificity and a simple free-radical oxidation reaction. The substrate site is 10 A from the iron (H202 site) and is probably just an oily droplet region of the protein. This proteins has parallels with Professor Klotz s systems. Proximity is perhaps sufficient to explain the activation of the organic substrate (but not for that of H2Oz). 

For foreign compounds, the majority of oxidation reactions are catalyzed by monooxygenase enzymes, which are part of the mixed function oxidase (MFO) system and are found in the SER (and also known as microsomal enzymes). Other enzymes involved in the oxidation of xenobiotics are found in other organelles such as the mitochondria and the cytosol. Thus, amine oxidases located in the mitochondria, xanthine oxidase, alcohol dehydrogenase in the cytosol, the prostaglandin synthetase system, and various other peroxidases may all be involved in the oxidation of foreign compounds. 

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