Multi oxidizing enzymes

Oxidizing Enzymes in Multi-Step Biotransformation Processes... 

The role of oxidative enzymes in existing multi-step processes can be considered in various different contexts, each of which are discussed below. These include ... 

Industrial and applied multi-step reaction processes, where oxidizing enzymes are components of industrial processes, include in the pulp and paper industry, in the food and beverage industry, for bioremediation, in biosensors and, more recently, in biofuel cells (discussed in more detail in Section 3.8). 

Examples of Multi-Enzyme Biotransformation Processes Involving Oxidizing Enzymes... 

The oxidation of pyruvate to acetyl CoA is accomplished by the Pyruvate Dehydrogenase complex, a large, multi-component enzyme with three main enzyme subunits. 

The most studied of all copper-confaining oxidases is cytochrome c oxidase of mitochondria. This multi-subxmif membrane-embedded enzyme accepts four elecfrons from cytochrome c and uses them to reduce O2 to 2 HjO. It is also a proton pump. Its structure and functions are considered in Chapter 18. However, it is appropriate to mention here that the essential catalytic centers consist of two molecules of heme a a and 3) and three Cu+ ions. In the fully oxidized enzyme two metal centers, one Cu + (of the two-copper center Cu ) and one Fe + (heme a), can be detected by EPR spectroscopy. The other Cu + (Cug) and heme exist as an EPR-silent exchange-coupled pair just as do the two copper ions of hemocyanin and of other t57pe 3 binuclear copper centers. 

Laccases (benzenediohoxygen oxidoreductases, EC 1.10.3.2) are a diverse group of multi-copper enzymes, which catalyze oxidation of a variety of aromatic compounds. Laccases oxidize their substrates by a one-electron transfer mechanism. They use molecular oxygen as the electron acceptor. The substrate loses a single electron and usually forms a firee radical. The unstable radical may undergo further laccase-catalysed oxidation or non-enzymatic reactions including hydration, disproportionation, and polymerisation. ... 

Thiamin has a central role in energy-yielding metabo-hsm, and especially the metabohsm of carbohydrate (Figure 45-9). Thiamin diphosphate is the coenzyme for three multi-enzyme complexes that catalyze oxidative decarboxylation reactions pymvate dehydrogenase in carbohydrate metabolism a-ketoglutarate dehydro-... 

Meat products have to be stabilised in some cases, as meat lipids contain no natural antioxidants or only traces of tocopherols. Most muscle foods contain, however, an efficient multi-component antioxidant defence system based on enzymes, but the balance changes adversely on storage. The denaturation of muscle proteins is the main cause of the inbalance as iron may be released from its complexes, catalysing the lipid oxidation. Salting contributes to the negative effects of storage, as it enhances oxidation. Using encapsulated salt eliminates the deleterious effect of sodium chloride. 

Of direct interest for biofuel cell applications are the reported reduction of O2 by multi-copper oxidases on carbon nanotube electrodes [Yan et al., 2006 Zheng et al., 2006] and the oxidation of H2 by hydrogenase covalently bound to carbon nanotubes [Alonso-Lomillo et al., 2007]. The hydrogenase/nanotube anode is extremely stable (>1 month), and shows 33-fold enhanced enzyme coverage compared with similarly treated graphite of the corresponding geometric surface area. A. vinosum... 

Compared with ketoreductases, the synthetic application of alcohol oxidases has been less explored. However, selective oxidation of primary alcohols to aldehydes is superior to the chemical methods in terms of conversion yields, selectivity, and environmental friendliness of reaction conditions. In addition, coupling of alcohol oxidase with other enzymes provides a tremendous opportunity to develop multi-enzyme processes for the production of complex molecules. Therefore, a growing impact of alcohol oxidases on synthetic organic chemistry is expected in the coming years. 

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