Catalase reaction mechanism

In the course of developing the idea of the enzymatic catalysis mechanism Poltorak [99] stated the uniformity of enzymatic catalysis mechanisms in the framework of suggested notion of linear chain of bond redistribution (linear CBR). Actually, this idea laid the foundation for the catalase reaction mechanism suggested by Poltorak. In this mechanism, owing to composition of linear CBRs he showed the means for effective proton transfer between... 

The chemistry of the colorful, perplexing, and challenging problem of catalase mechanism has been set forth in numerous reviews. Those by Brill 16), Nicholls and Schonbaum (f ), and most recently, Deisseroth and Bounce (15) summarize the fundamental properties of catalase and its reactions, and their physiological implications. Further, Feinstein 19) and Aebi 20-22) have presented detailed evaluations of acatalasemia, and de Duve 23) and others have discussed catalase biosynthesis 23-26), its intracellular location 23-25) and its turnover 24, 26-28). These facets of the catalase problem will not be reiterated. Instead, a brief synopsis of the enzyme characteristics will be followed by a discussion on the nature of the active site and the chemistry of the catalase reaction mechanism. 

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. 

Turnover numbers for some representative enzymes are listed in table 7.2. The enormous value of 4 x 107 mole-cules/s achieved by catalase is among the highest known the low value for lysozyme is at the other end of the spectrum. As is the case with Km, the relationship of kcal to individual rate constants, such as k2 and k3, depends on the details of the reaction mechanism. 

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],... 

Studies of hematin associates [94] indicate their inactivity in the catalase reaction. The interaction by the Fe-O-Fe mechanism, the existence of which was confirmed by the Mossbauer spectroscopy method, also disproves the idea of two hematin group interaction in the active site of catalase [92],... 

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. 

Figure 6.11 The formation mechanism of catalase reaction products, (a) The Oguri complex formed with the second H2Q molecule, (b) H20 and 02 formation, and native enzyme synthesis.

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

It is shown that with the model system [38, 59] heme iron reaction with hydrogen peroxide is promoted by acidic catalytic sites, which are replaced by distal amino acid group bound to heme [60], Here experimentally observed two-electron oxidation substrate in one stage and corresponded hydride-ion transfer is confirmed [61, 62], In the example of catalase reaction the transfer mechanism of two electrons simultaneously was discussed above... 

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. 

Abe K, Makino N, Anan FK (1979) pH dependency of kinetic-parameters and reaction-mechanism of beef-liver catalase. J Biochem 85 473-479... 

Haem proteins that react with oxygen also utilise ferryl intermediates. Fig. 4 compares the (proposed) reaction mechanisms of cytochrome oxidase and cytochrome P-450 with those of peroxidases and catalases. As can be seen, several of the reaction intermediates have the same oxidation states (although the protonation steps and stage at which H2O is released may be different). However, in contrast to peroxidases, oxidases must react with molecular oxygen, and this requires a reaction cycle that includes Fe11. 

Catalase contains four protein subunits, each of which contains a haem (Fe(III)-protoporphyrin) group within the active site. The active site of each subunit is stabilized by one molecule of tightly bound NADPH, and dissociation of the four subunits by freezing, or exposure to acid or alkali, results in complete loss of activity. The reaction mechanism is shown in Fig. 2. 

Figure 4. Schematic illustration of a possible mechanism for the catalase reaction in Mn catalase.

The central theme that the apoprotein facilitates the scission of the O—O bond is based on the established mechanisms of peroxide heterolysis 165). By invoking concerted proton transfer (s) in the transition state, such schemes illustrate that oxygen-oxygen heterolysis need not be attended by an electrostatically unfavorable charge separation. In addition, they offer some rationale for the observed high entropy of activation in the primary H202-catalase reaction (—25 cal mole" deg ) 166). This should be the case in a rigid lattice of interactions implied in Eq. (20) and formulas (VII) and (VIII). 

Reaction Mechanisms with the Catalase-Peroxide Complexes. 402... 

The noncompetitive inhibition of the decomposition of hydrogen peroxide by cyanide is not immediately obvious from the above reaction mechanism for if cyanide can compete in the formation of the peroxide complex which is responsible for the oxygen evolution in step IV, competitive inhibition might be expected. However, under the experimental conditions necessary to observe peroxide decomposition, an excess of peroxide is required and this is sufficient to give the maximal concentration of the peroxide complex, 1.2 or 1.6 moles of bound peroxide for each erythrocyte or bacterial catalase molecule respectively, i.e., the peroxide complex concentration is independent of the peroxide concentration. Analysis of the system under these conditions shows noncompetitive inhibition to hold. 

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