Peroxidases sources

Peroxidase Source Catalyzed Reaction Biological Functions... 

Heme Peroxidases Sources and Brief Review of Biochemical and... 

It should be noted that a number of different enzyme preparations can now be purchased directly from manufacturing chemists. It must be emphasised that the activity of an enzyme, whether purchased or prepared in the laboratory, may vary between rather wide limits. The activity is dependent on the source of the enzyme, the presence of poisons and also on the temperature. It appears, for example, that the quality of horseradish peroxidase depends upon the season of the year at which the root is obtained from the ground. It cannot be expected therefore that all the experiments described below will work always with the precision characteristic of an organic reaction proceeding under accurately known conditions. 

This enzyme Is widely distributed, more particularly in plants. Three important sources of the enzyme are horse-radish, turnips and milk. Peroxidase is capable of activating both hydrogen peroxide and a suitable substrate so that the latter is oxidised, although hydrogen peroxide alone may be incapable of affecting this change. It sometimes happens that hydrogen pcr-... 

In order for the cyclooxygenase to function, a source of hydroperoxide (R—O—O—H) appears to be required. The hydroperoxide oxidizes a heme prosthetic group at the peroxidase active site of PGH synthase. This in turn leads to the oxidation of a tyrosine residue producing a tyrosine radical which is apparendy involved in the abstraction of the 13-pro-(5)-hydrogen of AA (25). The cyclooxygenase is inactivated during catalysis by the nonproductive breakdown of an active enzyme intermediate. This suicide inactivation occurs, on average, every 1400 catalytic turnovers. 

Enzyme-mediated chiral sulfoxidation has been reviewed comprehensively in historical context [188-191]. The biotransformation can be mediated by cytochrome P-450 and flavin-dependent MOs, peroxidases, and haloperoxidases. Owing to limited stability and troublesome protein isolation, a majority of biotransformations were reported using whole-cells or crude preparations. In particular, fungi have been identified as valuable sources of such biocatalysts and the catalytic entities have not been fully identified in all cases. 

The peroxidase-catalyzed polymerization of m-alkyl substituted phenols in aqueous methanol produced soluble phenolic polymers. The mixed ratio of buffer and methanol greatly affected the yields and the molecular weight of the polymer. The enzyme source greatly affected the polymerization pattern of m-substituted monomers. Using SBP catalyst, the polymer yield increased as a function of the bulkiness of the substituent, whereas the opposite tendency was observed when HRP was the catalyst. 

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

Notes. When using biotin-labeled secondary antibodies instead of enzyme-labeled antibodies, you have first to detect biotin with enzyme-labeled (strept) avidin and proceed further with the Substrate Step (9). Do not add normal serum, non-fat dried milk, culture media or other potential sources of biotin to (strept)avidin-containing reagents. This may result in reduced sensitivity. Solutions containing sodium azide or other inhibitors of peroxidase activity should not be used in diluting the peroxidase substrate. 

In most terrestrial plant-pathogen interactions a diphenylene-iodonium (DPI)-sensitive (O Donnell et al. 1993), membrane-located, and receptor-activated NADPH oxidase generates superoxide radicals (Levine et al. 1994 Doke and Miura 1995 Lamb and Dixon 1997 Bolwell et al. 1998), which eventually dis-mutate into H202 and 02 (Sutherland 1991). Apoplastic peroxidases (Bolwell et al. 1998 Martinez et al. 1998), as well as various oxidases such as oxalate oxidase (Zhang et al. 1995 Thordal-Christensen et al. 1997) or amine oxidase (Laurenzi et al. 2001 Rea et al. 2002), have also been identified as sources of ROS in higher plants. 

Enzymatic hydroxylation of biological molecules is often catalyzed by hydroxylases. These types of enzymes are either oxygenases or peroxidases, in which the source of oxygen is O2 or H2O2, respectively. Cytochrome P-450-dependent enzymes represent a common class of enzymes that carry out hydroxylation reactions. L-Carnitine is a metabolite isolated from many organisms and its biosynthesis begins with the enzymatic hydroxylation of trimethyllysine. The intermediate, 3-hydroxyl-e-(A(A(ALtrimethyl)-L-lysine, is further... 

Sources and Biological Functions of Peroxidases Mechanisms of Peroxidase Catalysis. ... 

Peroxidases (E.C. 1.11.1.7) are ubiquitously found in plants, microorganisms and animals. They are either named after their sources, for example, horseradish peroxidase and lacto- or myeloperoxidase, or akin to their substrates, such as cytochrome c, chloro- or lignin peroxidases. Most of the peroxidases studied so far are heme enzymes with ferric protoporphyrin IX (protoheme) as the prosthetic group (Fig. 1). However, the active centers of some peroxidases also contain selenium (glutathione peroxidase) [7], vanadium (bromoperoxidase)... 

In recent years, numerous applications of such peroxidase-catalyzed oxidative coupling of phenols and aromatic amines have been reported (Table 7). These peroxidase-catalyzed biotransformations lead to modified natural products with high biological activities [110-118]. Several examples have also been described for the oxidative coupling of phenols with peroxidases and other oxidative enzymes from a variety of fungal and plant sources as whole cell systems... 

There are a few common enzymes that have been employed in these types of assay systems over the years, the chief among them being the peroxidase enzyme (3). Peroxidase has an oxidative function when in conjunction with a source of oxygen, transferring electrons to a molecule, which becomes oxidized. The peroxidase enzyme found in the horseradish plant has been used for its ability to carry out this function, for the fact that it is easily obtained, and for the antigenic differences from most mammalian forms of the enzyme. The oxidative function of this enzyme allows for the use of chromogens, which when oxidized, not only change color, but precipitate in such a manner as to render a permanent preparation. 

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