Peroxidases decomposition

Enzyme Decay. Moffett and Zafiriou (I) differentiated catalase- and peroxidase-mediated decay in coastal (marine) waters by using lsO-labeled H202 and 02, and by determining the labeled end products. Equation 13 shows that the products of catalase decomposition are H20 and 02. In contrast, peroxidase decomposition results in the formation of H20 without 02. From the measurement of the relative amount of labeled products it is possible to determine the contribution of both enzymes in the decay of the H202. In the coastal water, 65-80% of the decomposition was attributed to catalase and the rest to peroxidase (I). These studies are the first to use this technique. The approach should be extended to freshwater ecosystems to see if the same pattern would be found. 

The effects of lAA chloro-derivatives on the growth and the alkaloid production are presented in Fig. (36). Both lAA chloro-derivatives, 4-Cl-IAA and 5,6-Cl2-IAA, enhanced the growth of the roots compared with lAA at low concentrations. The optimum concentrations for alkaloid production were 0.1 mg/1 for 4-Cl-IAA and 0.01 mg/1 for 5,6-Cl2-IAA. The culture with 4-Cl-IAA (0.1 mg/1) or 5,6-Cl2-IAA (0.01 mg/1) resulted in a decrease of scopolamine and in a slight increase of hyoscyamine yield as compared with lAA, Figs. (35) and (36). It is known that 4-Cl-IAA and 5,6-Cl2-IAA are resistant to peroxidase decomposition [56] and the results indicate that they exert their effects at much lower concentrations than lAA. Thus they may be useful plant growth regulators for tropane alkaloid production in root cultures. 

One of the most used systems involves use of horseradish peroxidase, a 3-diketone (mosl commonly 2,4-pentandione), and hydrogen peroxide." " " Since these enzymes contain iron(II), initiation may involve decomposition of hydrogen peroxide by a redox reaction with formation of hydroxy radicals. However, the proposed initiation mechanism- involves a catalytic cycle with enzyme activation by hydrogen peroxide and oxidation of the [3-diketone to give a species which initiates polymerization. Some influence of the enzyme on tacticity and molecular... 

It participates in the decomposition of potentially toxic hydrogen peroxide in the reaction catalyzed by glutathione peroxidase (Ghapter 20). 

Glutathione-peroxidase (GSH-Pxase) is an enzyme found in erythroqrtes and other tissues that has an essential selenocysteine residue involved in the catalytic decomposition of reactive oxygen species. In the erythrocyte, hydrogen peroxide is the principle reactive oxygen species available. 

Concerning the mode of formation of ES, we prefer the concept that the substrate in a monolayer is chemisorbed to the active center of the enzyme protein, just as the experimental evidence pertaining to surface catalysis by inorganic catalysts indicates that in these reactions chemisorbed, not physically adsorbed, reactants are involved. Such a concept is supported by the demonstration of spectroscopically defined unstable intermediate compounds between enzyme and substrate in the decomposition by catalase of ethyl hydroperoxide,11 and in the interaction between peroxidase and hydrogen peroxide.18 Recently Chance18 determined by direct photoelectric measurements the dissociation con-... 

Chlorocatechols, known intermediates in the decomposition of 2,4-D,2,4,5-T, and other pesticides, were shown to be incorporated by enzymatic polymerization into HA when reacted with purified horseradish peroxidase. 

The Bombardier beetle possesses, at the end of its abdomen, a combustion chamber that contains a hydroqui-none and hydrogen peroxide. When a predator approaches, the cells in the walls of the combustion chamber secrete two enzymes, catalase and peroxidase. Catalase causes decomposition of hydrogen peroxide to produce oxygen peroxidase catalyses the oxidation of the hydroquinone to produce a quinone. 

Glutathione peroxidases catalyze the reductive decomposition of H202 or of organic peroxides by glutathione (G-SH) according to Eq. 15-58. At least three isoenzyme forms have been identified in mammals a cellular form,531 535-537 a plasma form, and a... 

H202 Determination. The analytical method for determination of H202 measures the loss in fluorescence of scopoletin by the peroxidase-mediated decomposition of H202 (11, 61-64). Separate standard curves were determined for each water or culture studied because the slope of the curve is affected by dissolved organic carbon (65, 66). 

Biological Decay. The two major enzyme systems that are used to control intracellular H202 concentrations in organisms are catalases and peroxidases (47). The different overall reactions for H202 decomposition mediated by these two enzyme systems can be illustrated as follows for catalase ... 

Another approach uses the coupling reaction of p-anisidine. In the presence of H202 and peroxidase (16), an oxidation product that contains two aromatic rings, benzoquinone-4-methoxyaniline, is formed stoichiometri-cally (92). Equations 14-16 indicate that an electron donor or hydrogen donor is required for peroxidase-mediated decomposition of H202. In two natural waters and one soil suspension, peroxidatic activity was identified by the stoichiometric removal of p-anisidine by the addition of H202 (in the dark) (16). This procedure provides an independent corroboration of the results obtained by Moffett and Zafiriou (1). However, this method does not quantify the relative importance of peroxidases versus catalases in the decomposition of H202. 

The two major enzyme systems that lead to the decomposition of H202 are catalases and the peroxidases. By using 1802, Moffett and Zafiriou (1) showed that catalase is responsible for 65-80% of the decomposition of H202 and that peroxidase-mediated decay accounts for 20-35% of the loss. These experiments have not been extended to freshwater systems, and therefore the relative contribution of the two enzyme systems has not been established. 

The treatment of peroxidases in the FeUI resting form with hydrogen peroxide gives a green species (for HRP) known as compound I, which is oxidized to a level of two equivalents above Fein. On slow decomposition, compound I is converted into a red product, compound II, which has one oxidizing equivalent above Fe111. In the presence of a substrate, compound I is reduced to compound II, and then compound II is reduced to the native enzyme (equations 71-73, where AH is a reducing substrate, and A the radical product which will react further). In some cases oxidation of substrate is a direct two electron process. 

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