Catalase peroxidatic activity

The next largest group of catalases are the catalase-peroxidases, so named because they exhibit a significant peroxidatic activity in addition to the catalatic activity. They have been characterized in both fungi and bacteria and resemble certain (type I) plant and fungal peroxidases... 

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. 

Both catalases and peroxidases can oxidize a variety of organic substrates (peroxidatic activity) (Reaction (5)) ... 

Catalase exerts a dual function (1) decomposition of HjOj to give H2O and O2 (catalatic activity) and (2) oxidation of electron donors, e.g., methanol, ethanol, formic acid, phenols, with the consumption of 1 mol of peroxide (peroxidatic activity) ... 

Brunelli L, Yermilov V, Beckman JS (2001) Modulation of catalase peroxidatic and catalatic activity by nitric oxide. Free Radic Biol Med 30 709-714... 

Some of these enzyme-substrate complexes, in a second reaction sequence, can oxidize a hydrogen donor molecule. If this donor happens to be HiOs we speak of catalatic activity, and if other hydrogen donors are oxidized, of peroxidatic activity. Catalase can exhibit both activities, whereas peroxidase can act only peroxidatically. 

That these mechanisms are valid has been concluavely shown by Chance (1-4), who studied the kinetics intensively by means of rapid optical methods that allow him to measure the rates of the separate reaction steps. He could show (4,101) that k[, the reaction constant for over-all catalase activity, is related to ki and k i of equations (4) and (5). But ki and 4 cannot be determined individually from the over-all reaction kinetics unless the ratio of the steady state concentrations of the enzyme-substrate compound to the free enzyme is known. In the case of peroxidatic activities where the substrate and donor are different molecules, their relative concentrations determine whether h or h is measured by the over-all activity usually an ill-de6ned mixture of the two reaction velocity constants is measured. The conditions appropriate for the evaluation of ki and kt from the over-all activity are discussed in a recent paper (4) by Chance, and the calculation of ki from the kinetics of peroxidase reactions and the standard peroxidase activity unit PZ (see p. 389) has also been carried out. Any sound procedure for activity determination should depend to as great an extent as possible upon the measurement of only one reaction velocity constant of the enzymic mechanism. 

This mechanism represents peroxidase action and the peroxidatic activity of catalase. 

Peroxidase and catalase are hemoproteins of wide distribution which catalyze the transfer of two electrons from substrates to hydrogen peroxide, forming water and oxidized donors (1,143,150,266,276, 483,749,751). During catalatic oxidation a second molecule of hydrogen peroxide supplies two electrons, and is oxidized to oxygen (equar tion 28) (137). Peroxidatic oxidation refers to the enzymic reduction of hydrogen peroxide to water by electron donors other than peroxide (equation 29). Catalase has peroxidatic activity at low concentrations of hydrogen peroxide (4a,397,402,742). 

Manganous ions activate peroxidase as an oxidase toward oxalate, oxalacetate, ketomalonate, and dihydroxytartrate. A peroxidase substrate is necessary for the reaction with the first two substrates, but not for the last two. These reactions depend upon the presence of peroxide. They can be facilitated by adding peroxide, or inhibited by adding catalase, but it is uncertain whether they are instances of direct oxidase action, or of peroxidatic activity (414). 

A similar system to that for dicarboxylic acids has been described by Akazawa and Conn (1958) for pyridine nucleotides. Chance (1951) had shown that DPNH was a hydrogen donor for the peroxidatic activity of the enzyme, albeit not a very effective one. Akazawa and Conn found that an oxidatic reaction was also catalyzed by peroxidase if manganous ions and a monohydric phenol were present. In its sensitivity to catalase, copper salts, and cyanide, this system closely resembles the classical peroxidase-catalyzed oxidations. Although these investigators did not analyze their system in the terms put forward by Yamazaki, they found that oxidogenic donors were stimulatory and redogenic donors inhibitory in this reaction. 

This enzyme occurs in plants, animals, and microorganisms. The molecule has four subunits each of these contains a protohemin group, which forms part of four independent active sites. The molecular weight is 240,000. Catalase is less stable to heat than is peroxidase. At neutral pH, catalase will rapidly lose activity at 35°C. In addition to catalyzing the reaction shown above (catalatic activity), catalase can also have peroxidatic... 

These are difficult enzymes to work with and only recently have crystal structures become available for two catalase-peroxidases Haloarcula marismortui (HMCP) and Burkholderia pseudomallei (BpKatG). A typical subunit is approximately 80 kDa in molecular mass, with a single heme b prosthetic group. The primary structure of each subunit can be divided into two distinct domains, N terminal and C terminal. The N-terminal domain contains the heme and active site, while the C-terminal domain does not contain a heme binding motif and its function remains unclear. The clear sequence similarity between the two domains suggests gene duplication and fusion. Curiously, despite many years of study, the actual in vivo peroxidatic substrate of the catalase-peroxidases has not been identified. 

Two pathways have been described for formate metabolism a peroxidatic pathway via catalase and a folate dependent one carbon pathway. Treatment of rats with amino-triazole, an irreversible inhibitor of catalase, severely depressed a-oxidation activity but only slightly decreased the production of CO2 from exogenously added formate. " Whether the effect of aminotriazole is (solely) linked to the inhibition of catalase is unclear (see further). In addition to these above mentioned pathways our data point to a cytosolic NAD -dependent dehydrogenase activity that acts on the formate produced during a-oxidation. In peimeabilized cells or broken systems, suppUed with the qi-propriate cofactors (see further), almost no CO2 is formed, during a-oxidation unless NAD is added. ... 

It should be noted that it is not always possible to satisfy the inequalities kiXo kiOa and x<,< oo, for this implies that ki kt. With polyphenols and aminophenols, as donors for horseradish peroxidase, this is usually not possible, but with less active donors, such as phenol, p-aminobenzoic acid, ascorbic acid, and nitrous acid (near neutral pH), the requirement At is satisfied and zero-order kinetics are obtained (see Table VI in reference 3). If catalase reacts peroxidatically, alcohols and nitrous and formic acids (at neutral pH) satisfy the inequality. 

In addition to activities ordinarily ascribed to them, peroxidase and catalase possess properties as oxygen transferases and mixed function oxidases. They may exist in functionally active ferrous forms which have, like hemc lobin and myoglobin, the property of combining with molecular oxygen. This oxygen may be transferred to substrate, or be reduced in steps. For purposes of the present review, mechanisms that have been proposed for peroxidatic and catalatic oxidations will be summarized and followed by discussion of dihydroxyfumaric acid oxidase, tryptophan oxidase, and indolyl-acetic oxidase and related oxidases, and indole oxidase. All of these have properties in common with peroxidase and catalase. 

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