Peroxidases side reactions

Other peroxidases have a similar mechanism, but peroxidases vary significantly in terms of their rate constants and their susceptibility to side reactions that may cause temporary or permanent inactivation. 

The use of organic solvents is an alternative to enhance availability of hydrophobic substances, either substrates or products of the reaction, as well as to reduce side reactions. The first studies of peroxidase catalysis in water-miscible and water-immiscible organic solvents were initiated by Dordick and Klibanov using commercial HRP, one of the most often investigated enzymes [60, 61]. Several studies have been focused on the effect of solvents in peroxidase structure and function... 

As enantiomericaUy pure sulfoxides are excellent chiral auxUiaries for asymmetric synthesis, different approaches for biocatalytic asymmetric oxidations at the S-atom have been explored [30, 31]. Asymmetric peroxidaseorganic sulfides to sulfoxides in organic solvents opens up attractive opportunities by increased substrate solubility and diminished side reactions [32]. Plant peroxidases located in the cell wall are capable of oxidizing a broad range of structurally different substrates to products with antioxidant, antibacterial, antifungal, antiviral, and antitumor activities [33]. Hydroperoxides and their alcohols have been obtained in excellent e.e. in the biocatalytic kinetic resolution of secondary hydroperoxides with horseradish and Coprinus peroxidase [34]. 

These side reactions of superoxide dismutase are generally of no biological significance (except for a possibility in pathology, see Sect. 1.9). Nevertheless, they may be important under peculiar conditions e.g., due to its peroxidase activity, SOD may increase rather than decrease oxidation of a detector of reactive oxygen species [68]. The oxidation rate of a popular probe used for detection of reactive oxygen species, 2, 7 -dichlorofluorescin, is considerably augmented by CuZnSOD, especially in the presence of bicarbonate [67]. 

Recently, we have developed a method based on ABTS" generated by horseradish peroxidase (HRP) that permits the evaluation of the antioxidant activity of pure compounds and plant-derived samples.The method is easy, accurate, and fast to apply and presents numerous advantages because it avoids undesirable side reactions, does not require high temperatures to generate ABTS radicals, and allows for antioxidant activity to be studied over a wide range of pH values. This method is capable of determining both hydrophilic (in buffered media) antioxidant activity (HAA) and lipophilic (in organic media) antioxidant activity (LAA). In the second case. 

A method that was introduced by Kittl and co-workers in 2012 measures a side reaction of a PMO that seems of no further importance in the cellulose degradation process. In the absence of cellulose especially, the enzyme reduces O2 to H2O2 (Figure 3.6). Coupling of this reaction to the reduction of amplex red to resorufin in assistance of horseradish peroxidase (HRP), results in an assay where the formation of the fluorescent resorufin is proportional to the quantity of PMO added. The only electron donors tested in this reaction were cellohiose dehydrogenase (CDH) with addition of lactose to he reduced and ascorbate. The reaction is selective and sensitive to the... 

Successful work with peroxidases requires knowledge about the possible side reactions in the catalytic cycle. The most important are shown in Scheme 5 [39]. The pathway from 18 to 21 covers the normal catalytic cycle. If the local phenol concentration is too low and/or the local concentration of hydrogen peroxide is too high, compound I is converted into an intermediate (Scheme 5, 23) [39,69]. This intermediate can follow three different paths of decomposition. First it can react back to the na-... 

Scheme 5 Side reactions in the peroxidase catalytic cycle... 

The oxidase reaction is inhibited by carbon monoxide and by catalase, properties which are characteristic of oxidase-peroxidases, and which suggest that both ferrous iron and hydrogen peroxide participate in the overall reaction. If this is the case, inhibition by catalase may be explained by (1) destruction of hydrogen peroxide necessary to initiate the formation of ferroperoxidase, corresponding to the reduction of ferricatalase to ferrocatalase in the presence of peroxide and an electron donor (752), ) a side reaction in which oxyferroperoxidase is reduced to ferriperoxidase via Complex II (compare Fig. 17), or (S) destruction of peroxidase. In support of the last alternative, it has been observed that the decomposition of peroxide-... 

Peroxidase can be activated by a thermostable factor in pea seedlings to be a direct oxidase toward phenylacetaldehyde (413). Purified horse-radish peroxidase plus manganous ions behaves similarly toward this substrate. In either case, benzaldehyde and formic acid are the primary products, but the oxygen stoichiometry of the reaction is obscured by side reactions. Catalase has an inhibiting effect, which suggests that peroxide is an obligatory intermediate or activator. 

Yamazaki (1961) has recently suggested that the reduction of peroxidase to a ferrous form inhibited by carbon monoxide, and the formation of compound III, may both be side reactions produced by free radicals... 

Side-Chain Cleavage Reactions of 0-1 and fl-O-4 Lignin Model Compounds Catalyzed by Lignin Peroxidase. 

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