Catalase catalysis

Schiff base fonnation, photochemistry, protein partitioning, catalysis by chymotrypsin, lipase, peroxidase, phosphatase, catalase and alcohol dehydrogenase. 

Z. Zhang, S. Chouchane, R.S. Magliozzo, and J.F. Rusling, Direct voltammetry and catalysis with Mycobacterium tuberculosis catalase-peroxidase, peroxidases, and catalase in lipid films. Anal. Chem. 74,163-170 (2002). 

V. Mechanism of Catalysis by Tetraamide Macrocyclic Fem-TAML Activators of Hydrogen Peroxide, Functional Catalase-Peroxidase... 

Scheme 6. General mechanistic picture of catalysis by Fem-TAML activators of peroxides that underscores the peroxidase-like (peroxida-tic) and catalase-like (catalatic) activities of the catalysts. Here, S(red) is an oxidizable target substrate. All rate constants are conditional (pH dependent).

This reaction can be catalyzed in other ways by the enzyme catalase (see enzyme catalysis in Chapter 10), in which EA is 50 kJ mol-1, and by colloidal Pt, in which EA is even lower, at 25 kJ mol-1. 

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-... 

The heme of catalases is deeply buried within the core of the catalase subunit. Protoheme IX or heme b is found in all small-subunit catalases so far characterized. The two large-subunit enzymes HPII and PVC have been characterized biochemically, spectrally, and structurally 91) as containing heme d in which ring HI is oxidized to a cis-hydroxyspirolactone. Heme b is initially bound to both enzymes during assembly, and it is subsequently oxidized by the catalase itself during the early rounds of catalysis 92). 

Mechanisms of catalase and peroxidase catalysis. Attention has been focused on a series of strikingly colored intermediates formed in the presence of substrates. When a slight excess of H202 is added to a solution of horseradish peroxidase, the dark brown enzyme first turns olive green as compound I is formed, and then pale red as it turns into compound II. The latter reacts slowly with substrate AH2 or with another H202 molecule to regenerate the original enzyme. This sequence of reactions is indicated by the colored arrows in Fig. 16-14, steps a-d. 

The importance, for catalytic activity, of metal sites exhibiting different coordination environments has been evaluated by using asymmetrically coordinated dinuclear species [103b]. A mixture of l,4,7-trimethyl-l,4,7-triazacyclono-nane (Me3tacn) and bpy yielded bis(p-oxo)p-carboxylato) [Me3(tacn)MnmMnIV (bpy)], 54, the first such complex. This was indeed catalytically active, but still at the same low level (105 slower than catalase) as other symmetrical models. Nevertheless, the requirement for two metals for catalysis was confirmed since decomposition of the dinuclear species yields inactive, but similarly coordinated mononuclear complexes. 

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 area between enzymatic and chemical catalyses, associated with simulation of biochemical processes by their basic parameters, is accepted as mimetic catalysis. The key aspect of the mimetic catalyst is diversity of enzyme and biomimetic function processes, which principally distinguishes the mimetic model from traditional full simulation. Based on the analysis of conformities and diversities of enzymatic and chemical catalysis, the general aspects of mimetic catalysis are discussed. An idealized model of the biomimetic catalyst and the exclusive role of the membrane in its structural organization are considered. The most important achievements in the branch of catalysis are shown, in particular, new approaches to synthesis and study of biomimetic catalase, peroxidase and monooxidases reactions. 

Using crystalline cytochrome-c peroxidase [38] and catalase [39], it is shown that intermediates are formed according to the general mechanism of acidic-basic catalysis ... 

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