Catalase enzyme efficiency

The size and enzyme composition of peroxisomes vary considerably in different kinds of cells. However, all peroxisomes contain enzymes that use molecular oxygen to oxidize various substrates, forming hydrogen peroxide (H2O2). Catalase, a peroxisome-localized enzyme, efficiently decomposes H2O2 into H2O. Peroxisomes are most abundant in liver cells, where they constitute about 1 to 2 percent of the cell volume. 

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. 

Enzymes are exceptionally efficient catalytic proteins which increase the speed of a chemical reaction without themselves undergoing a permanent change. Under optimal conditions, most enzymatic reactions proceed from 10 to 10 times more rapidly than the corresponding non-enzymatic reactions. For example, one molecule of catalase, the enzyme which converts hydrogen peroxide into water and atomic oxygen, is able to deal with approximately 5 million molecules of H2O0 per minute. 

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... 

In contrast, antioxidant enzymes can efficiently counteract all UV-induced ROS (Aguilera et al. 2002). These enzymes are represented by superoxide dismutase (SOD), catalase and glutathione peroxidase as well as those involved in the ascorbate-glutathione cycle, such as ascorbate peroxidase, mono-dehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase. One of the most important classes of antioxidant enzymes is the SOD family, which eliminate noxious superoxide radical anions. Different metalloforms of SOD exist (Fe, Mn, CuZn and Ni), which due to their intracellular localisation protect different cellular proteins (Lesser and Stochaj 1990). 

Turning to l-AAO, Pantaleone s industrial research group have reported" on the properties and use of an l-AAO from Proteus myxofaciens, overexpressed in Escherichia coli This l-AAO, unusually, appears not to produce H2O2 in the catalytic reaction, thus making the addition of catalase unnecessary. The enzyme has a broad specificity, with a preference for nonpolar amino acids. This l-AAO was used in conjunction with a D-amino acid transaminase (d-AAT) and an alanine racemase (AR) to allow an efficient conversion of L-amino acid in to D-amino acid (Scheme 4). 

On the basis of the structure of their active site, catalases may be classified as heme or nonheme enzymes. Those that contain heme iron are efficient catalysts, operating close to the diffusion limit, 108M 1sec 1. In iron catalases the metal is coordinated by four heme nitrogens and a proximal Tyr residue, which occupies the fifth coordination site. A catalytically required His is found on the distal side of the heme. In addition, a water molecule has also been observed close to the iron sixth coordination site. 

Complex 52 is similar to Mn-catalase in that it is azide insensitive and forms a MnnMnm species on addition of hydroxylamine and a MnIIIMnIV catalyti-cally inactive form with an EPR spectrum closely resembling that of the enzyme. Importantly, the complex maintains its dinuclear structure in solution, while cycling between the MnnMnn, MnmMnm oxidation states and shows a good catalytic rate (kcat = 13 1 sec-1) and stability (>1000 turnovers). Catalases, however, are approximately 3000 times more efficient. 

Protein aggregates [107, 109, 121] or dye crystals [122-126] can serve as templates for LbL polyelectrolyte adsorption. Chymotrypsin aggregates encapsulated by PSS and PAH deposition contain a high protein amount and the enzyme keeps its bioactivity [107], The aggregates prepared in this manner have high incorporation efficiency and a protein content of 50-70% [109]. An encapsulated catalase has been shown to be stable against protease degradation [121],... 

Catalase, a heme-containing enzyme with tyrosine as the proximal heme ligand, decomposes hydroperoxides and peracids by this reaction. Catalase is one of the most efficient enzymes known, with maximum turnover numbers on the order of 107 s 1. In... 

Enzymes are protein molecules of colloidal size, somewhere between the molecular homogeneous and the macroscopic heterogeneous catalyst. Thus they are neither but somewhere in between. Enzymes are, of course, the driving force for biochemical reactions. Present in life processes, they are characterized by tremendous efficiencies and sclectivities. An enzyme, catalase, decomposes HjO 10 times faster than any inorganic catalyst. ... 

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