Peroxidase reaction mechanism

The analogy of catalase and non-classical peroxidase reaction mechanisms. 

As one may expect from the peroxidase reaction mechanism described in Eqs. (2-4), the reactivity of the enzyme intermediates towards a particular substrate may be estimated a priori on the basis of the thermodynamic driving force of these two electron-transfer reactions, which is directly related with the difference between the oxidation/reduction potentials of both the enzyme active intermediates (i.e.. Col and Coll) and the substrate radicals. Thus, the thermodynamic driving force for the reaction of Col (or Coll) with the reducing substrates is the difference between the mid-point potentials of the CoI/CoII (or CoII/Felll) and the substrate radical/substrate (R, Hr/RH) redox couples ... 

DET calculations on the hyperfine coupling constants of ethyl imidazole as a model for histidine support experimental results that the preferred histidine radical is formed by OH addition at the C5 position [00JPC(A)9144]. The reaction mechanism of compound I formation in heme peroxidases has been investigated at the B3-LYP level [99JA10178]. The reaction starts with a proton transfer from the peroxide to the distal histidine and a subsequent proton back donation from the histidine to the second oxygen of the peroxide (Scheme 8). 

When looking at the reaction mechanisms of glutathione peroxidase and isopenicillin N synthase, we did not find any reaction step where the transition state is significantly stabilized by long-range electrostatic interactions (i.e. electrostatic interactions outside the active-site model). However, it is should be added that most transition states have been calculated using ONIOM-ME. 

Gosh et al. reported LDA(SVWN) studies of oxo(porphyrinato)iron(IV) complexes.83 These compounds have been detected in various peroxidases and are believed to be involved in the reaction mechanisms of other heme enzymes, such as cytochromes P450. Very Good Fe-0 distance and values of unsealed stretching frequencies, which were in excellent agreement with CASSCF results, published elsewhere, were obtained. 

Compounds I and II are quite stable at low temf>erature and therefore can serve as pure reactants to study the mechanisms of peroxide oxidase processes (Douzou, 197la,b). When compound II reacted with indole 3-acetate, this compound was immediately regenerated without the appearance of any other intermediary compound. Moreover, indole 3-acetate in large excess induced the conversion of compound III into compound II. A study of reaction mechanisms of indole 3-acetate degradation by various peroxidases was recently carried out by Ricard and Job (1974) using low-temperature spectroscopic techniques. They obtained new data that made it possible to propose electronic mechanisms of reactions less speculative than those dependent upon data obtained under normal conditions of temperature. 

The catalase-peroxidases present other challenges. More than 20 sequences are available, and interest in the enzyme arising from its involvement in the process of antihiotic sensitivity in tuherculosis-causing bacteria has resulted in a considerable body of kinetic and physiological information. Unfortunately, the determination of crystallization conditions and crystals remain an elusive goal, precluding the determination of a crystal structure. Furthermore, the presence of two possible reaction pathways, peroxidatic and catalatic, has complicated a definition of the reaction mechanisms and the identity of catalytic intermediates. There is work here to occupy biochemists for many more years. 

We should also note that there are other ways in which substances can luminesce (/.e., produce light). One of the most common nonfluorescent mechanisms is called chemiluminescence. Chemical reactions can produce light when radicals (/.e., atoms or molecules with reactive unpaired electrons) combine to form a covalent bond. Heating of molecules can also cause them to display chemiluminescence. And, of course, there are biological processes that are accompanied by chemiluminescence. The most familiar case is the luciferase reaction associated with fire flies and luminescent marine creatures. Peroxidase reactions also produce faint luminescence. 

Yamasaki, H., Sakihama, Y., and Ikehara, N., Flavonoid-peroxidase reaction as a detoxification mechanism of plant cells against H2O2, Plant Physiol, 115, 1405, 1997. 

De Rycker, J. Halliwell, B. (1978) Oxidation of 2-nitropropane by horseradish peroxidase. Involvement of hydrogen peroxide and of superoxide in the reaction mechanism. Biochem. J., 175, 601-606... 

Ricard, J. and Job, D., 1974, Reaction mechanisms of indole-3-acetate degradation by peroxidases. A stopped-flow and low-temperature spectroscopic study, Eur. J. Biochem. 44 359-374. 

Laurenti E, Ghibaudi E, Ardissone S, Ferrari RP (2003) Oxidation of 2,4-Dichlorophenol Catalyzed by Horseradish Peroxidase Characterization of the Reaction Mechanism by UV-Visible Spectroscopy and Mass Spectrometry. J Inorg Biochem 95 171... 

FIGURE 9.13 Proposed reaction mechanism for H202 activation in horseradish peroxidase. (See the color version of this figure in Color Plates section.)... 

FIGURE 9.13 Proposed reaction mechanism for H202 activation in horseradish peroxidase. 

In the context of the above, the authors suggest that consideration of catalase and non-classical peroxidase reactions from positions of the ability of H202 to induce chemical conjugation in oxidation reactions broadens our knowledge about the role and mechanism of catalases and peroxidases. 

Not all aspects of biooxidation with the hydrogen peroxide mechanism in the presence of catalase are clear yet. The following mechanism is accepted in the biochemical literature [82], which illustrates formal iron valences in catalase and peroxidase reactions ... 

Of special importance is the example of catalase interaction with formate ion [87], because it represents a substrate for non-classical peroxidase reaction and, probably, the interaction mechanism between formate ion and Fe5+ complex is identical to the reaction mechanism with H202 [82],... 

Critically analyzing the mechanism (6.8)-(6.12), one may note the unsuitability of the currently presented interaction between complexes E-Fe3+—OH and E-Fe3+ OOH and substrates (H202 and H2D), because it is unclear how the substrate is activated. Moreover, intensification of the catalase reaction induces a non-classical peroxidase activity increase in ethanol and formic acid oxidation reactions. This indicates the existence of a unit common to these two processes [82, 83], The alternative action of catalase (catalase of peroxidase reaction) in the biosystem with solidarity of elementary stage mechanisms should be noted [88, 89], Peroxidase action of catalase requires a continuous supply of H202 for ethanol and formic acid oxidation, which can be explained by oxidation according to conjugated mechanism [90],... 

As mentioned above, the mechanisms of catalase and peroxidase reactions are similar at particular stages, and differences are observed at the stage of final alternative product formation ... 

Figure 6.3 shows catalase transformation under the substrate (ROOH) effect in complex II to be the predominant pathway. For neutral substrates, which are hydroperoxides, the rate of complex II formation is independent of pH and is usually described by the second-order equation [103, 104], Complex II is the general intermediate for catalase and peroxidase reactions with the only difference that for catalase it is colored green (unpaired electron is localized on heme) and for peroxidase it is red (unpaired electron is localized on distal amino-acid fragment). Complex III is also colored red for peroxidase. However, the formation mechanism is different. Complexes II, III and IV are typical of peroxidases, whereas for catalase only complex II is formed. At the stage of complex II formation, the general properties and distinctive features of catalase and peroxidase were determined. 

Further reduction of the catalase complex VI is shown in Figure 6.5 (peroxidase reaction) and Figure 6.6 (catalase reaction). These diagrams show that peroxidase and catalase reactions of catalase proceed by two-electron transfer mechanism in one stage and are practically equal. 

The authors of the present monograph suggested [108] a nontrivial mechanism of catalase and non-classical peroxidase reactions using BRC complexes in the design. 

The mechanisms of catalase and non-classical peroxidase reactions shown in Figures 6.11 and 6.13 explain a sequence of observable key factors ... 

Figure 6.13 The mechanism of non-classical peroxidase reaction. B is acidic or basic site.

By analogy with the mechanism of the catalase reaction, the probable mechanism of the peroxidase reaction is considered (Figure 8.12). Note that a proton transferred to the active site of the biomimetic electrode can be replaced by H+ from the reaction mixture volume. The mechanisms of catalase and peroxidase reactions provide an insight into the ways of their realization in the electrochemical mode. The ratio of products synthesized in both reactions (02 and CH3CHO) depends on the ratio of the H202 and CH3CHO interaction rates with the surface intermediate. 

Wirstam M, Blomberg MRA, Siegbahn PEM (1999) Reaction mechanism of compound I formation in heme peroxidases a density functional theory study. J Am Chem Soc 121 10178-10185... 

Blodig W, Smith AT, WA D et al (2001) Crystal structures of pristine and oxidatively processed lignin peroxidase expressed in Escherichia coli and of the W171F variant that eliminates the redox active tryptophan 171. Implications on the reaction mechanism. J Mol Biol 305 851-861... 

Another important aspect of peroxidase reactions is the relation between the substrate one-electron redox potential and the redox potential of compound I and compound II, since this restricts the number of possible redox partners (see Chap. 4 for a detailed description). Table 6.1 reports the redox potentials of some selected peroxidases as it can be seen, the values span an interval ranging from 1.35 V for reduction of myeloperoxidase (MPO) compound I to 1.0 V for reduction of HRP compound I [13-15]. But the selection of the preferred enzyme for a given radical reaction must consider not only the complementarities in the redox potentials but also the mechanism preferred by the enzyme, since some peroxidases, such as CPO and MPO, and also LPO in some cases, react through a two-electron oxidation mechanism. 

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