Enzymes catalases

N—Fe(IV)Por complexes. Oxo iron(IV) porphyrin cation radical complexes, [O—Fe(IV)Por ], are important intermediates in oxygen atom transfer reactions. Compound I of the enzymes catalase and peroxidase have this formulation, as does the active intermediate in the catalytic cycle of cytochrome P Q. Similar intermediates are invoked in the extensively investigated hydroxylations and epoxidations of hydrocarbon substrates cataly2ed by iron porphyrins in the presence of such oxidizing agents as iodosylbenzene, NaOCl, peroxides, and air. 

The term represents the kinetic efficiency of the enzyme. Table 14.4 lists turnover numbers for some representative enzymes. Catalase has the highest turnover number known each molecule of this enzyme can degrade 40 million molecules of HgOg in one second At the other end of the scale, lysozyme requires 2 seconds to cleave a glycosidic bond in its glycan substrate. 

In this reaction, hydrogen peroxide is produced which is toxic to cells and has to be removed quickly and efficiently. This is carried out by the enzyme catalase. The C°wrafion equation also indicates the need for molecular oxygen and the fermentation process needs a continuous supply of air. 

Superoxide is formed (reaction 1) in the red blood cell by the auto-oxidation of hemoglobin to methemo-globin (approximately 3% of hemoglobin in human red blood cells has been calculated to auto-oxidize per day) in other tissues, it is formed by the action of enzymes such as cytochrome P450 reductase and xanthine oxidase. When stimulated by contact with bacteria, neutrophils exhibit a respiratory burst (see below) and produce superoxide in a reaction catalyzed by NADPH oxidase (reaction 2). Superoxide spontaneously dismu-tates to form H2O2 and O2 however, the rate of this same reaction is speeded up tremendously by the action of the enzyme superoxide dismutase (reaction 3). Hydrogen peroxide is subject to a number of fates. The enzyme catalase, present in many types of cells, converts... 

Enzymes are nature s catalysts. For the moment it is sufficient to consider an enzyme as a large protein, the structure of which results in a very shape-specific active site (Fig. 1.3). Flaving shapes that are optimally suited to guide reactant molecules (usually referred to as substrates) in the optimum configuration for reaction, enzymes are highly specific and efficient catalysts. For example, the enzyme catalase catalyzes the decomposition of hydrogen peroxide into water and oxygen... 

As an example, we mention the enzyme catalase, which catalyzes the decomposition of H2O2 to H2O and O2 at a turnover number of kcat = 10 and a high specificity constant of kcat/f M = 4 x 10 mol s . Such activities are orders of magnitude higher than those of heterogeneous catalysts. 

Garlic s proven mechanisms of action include (a) inhibition of platelet function, (b) increased levels of two antioxidant enzymes, catalase and glutathione peroxidase, and (c) inhibition of thiol enzymes such as coenzyme A and HMG coenzyme A reductase. Garlic s anti-hyperlipidemic effects are believed to be in part due to the HMG coenzyme A reductase inhibition since prescription medications for hyperlipidemia have that mechanism of action (statins). It is unknown whether garlic would have the same drug interactions, side effects, and need for precautions as the statins. 

Fig. 7.n SEM images of the 3D macroporous functionalized macroporous zeolitic membrane zeolitic membrane used as a support for enzyme bioreactor was prepared via the LbL electrostatic immobilization by the LbL procedure. Images assembly of PEs and enzyme (catalase) on the 3D (A-D) are cross-sections of the membrane at macroporous membrane. (Reprinted from [59] different magnifications. A biomacromolecule- with permission of Wiley-VCH). 

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. 

In the Thought Lah above, you may have included the enzyme catalase in your brainstormed list. Catalase in your blood is responsible for the fizzing you see when you use a dilute hydrogen peroxide solution to disinfect a cut. When dilute hydrogen peroxide is poured on a cut, it decomposes to oxygen gas and water. The decomposition reaction is catalyzed by catalase. 

The enzyme catalase is contained in human, animal, and plant tissues. 

The iron enzymes catalase and peroxidasepromote these reactions very effectively, but it is unlikely that both reactants are coordinated to the metal during the reaction. It is generally true that the metal site is restricted in enzymes, allowing coordination of only one reactant. The other reactant is however often held close by the protein structure. 

Todd, G. W. Effect of low concentrations of ozone on the enzymes catalase, peroxidase, papain and urease. Physiol. Plant. 11 457-463, 1958. 

Peroxisomes are spherical vesicles bounded by a single membrane. They contain enzymes that catalyse oxidations that produce hydrogen peroxide which is degraded by the enzyme catalase. For example, very long or unusual fatty acids that are present in the diet but have no function are completely degraded in the peroxisomes. 

The catalysts are enzymes, most of which are proteins. Not only are they catalysts, bnt their catalytic powers are enormous they can increase the rate of a reaction by several orders of magnitnde. Indeed, in the absence of enzymes, life as we know it wonld not be possible. One remarkable example of the nse of the catalytic power of two enzymes in biology is the Bombardier beetle it uses the enormous catalytic power of the enzymes catalase and a peroxidase to deter predators (Box 3.1). 

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. 

The H2O2 is decomposed by the enzyme catalase which occnrs in the peroxisomes ... 

An elegant four-enzyme cascade process was described by Nakajima et al. [28] for the deracemization of an a-amino acid (Scheme 6.13). It involved amine oxidase-catalyzed, (i )-selective oxidation of the amino acid to afford the ammonium salt of the a-keto acid and the unreacted (S)-enantiomer of the substrate. The keto acid then undergoes reductive amination, catalyzed by leucine dehydrogenase, to afford the (S)-amino acid. NADH cofactor regeneration is achieved with formate/FDH. The overall process affords the (S)-enantiomer in 95% yield and 99% e.e. from racemic starting material, formate and molecular oxygen, and the help of three enzymes in concert. A fourth enzyme, catalase, is added to decompose the hydrogen peroxide formed in the first step which otherwise would have a detrimental effect on the enzymes. 

The enzyme catalase effectively decomposes hydrogen peroxide... 

Hydrogen peroxide is used as a sterilant or preservative for milk and whey it destroys harmful micro-organisms. Any excess hydrogen peroxide left in the milk or whey after treatment can be decomposed to water and oxygen using an enzyme (catalase). 

Acyl CoA oxidase, which is induced up to at least 15 X normal levels, catalyzes a specific step characteristic of jl-oxidation in the peroxisome-producing hydrogen peroxide as a byproduct (Fig. 7.10). Other oxidases may also lead to increased hydrogen peroxide. Normally, this is removed and detoxified by the enzyme catalase, which breaks hydrogen peroxide down to water and oxygen. However, catalase is only increased about twofold after treatment with peroxisomal proliferators. 

Structure and use of porphyrins Porphyrins are cyclic compounds that readily bind metal ions—usually Fe2+ or Fe3+ The most prevalent metalloporphyrin in humans is heme, which is found in hemoglobin, myoglobin, cytochromes, and the enzymes catalase and tryptophan pyrrolase. 

The first reduction wave in the d.c. polarogram of oxygen is increased in the presence of the enzyme catalase [11]. This is caused by the dismutation of the produced hydrogen peroxide into oxygen and water (H202 = H20 + i 02 ). 

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