Oxidoreductases and Oxygenases

Oxidoreductases (dehydrogenases or oxidases) catalyze the addition or the removal of hydrogen or electrons. Oxygenases bring about the incorporation of oxygen which originates from molecular oxygen. 

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Similarly, many oxygenation reactions (Table 2.1), which also require cofactors, are usually performed using whole micro-organisms. Collectively, oxidoreductases and oxygenases account for around 30% of all reported biotransformations. 

The cellular destruction of grapes during pre-fermentation treatments results in oxygen dissolution, despite the precautions taken. Two enzyme categories, oxidoreductases and oxygenases, are responsible for many grape constituent transformations. They often harm grape quality. 

Oxidoreductases have a variety of functions in metabolism oxidases and dehydrogenases play major roles in respiration hydroperoxidases protect the body against damage by free radicals and oxygenases mediate the hydroxylation of drugs and steroids. 

A broad spectrum of chemical reactions can be catalyzed by enzymes Hydrolysis, esterification, isomerization, addition and elimination, alkylation and dealkylation, halogenation and dehalogenation, and oxidation and reduction. The last reactions are catalyzed by redox enzymes, which are classified as oxidoreductases and divided into four categories according to the oxidant they utilize and the reactions they catalyze 1) dehydrogenases (reductases), 2) oxidases, 3) oxygenases (mono- and dioxygenases), and 4) peroxidases. The latter enzymes have received extensive attention in the last years as bio catalysts for synthetic applications. Peroxidases catalyze the oxidation of aromatic compounds, oxidation of heteroatom compounds, epoxidation, and the enantio-selective reduction of racemic hydroperoxides. In this article, a short overview... 

In the field of bioremediation, oxidoreductases are considered to be excellent biocatalysts for environmentally friendly processes. Laccases and peroxidases are widely used to treat effluents from pulp/cotton mills, food/fruit processing plants and breweries [1, 2, 37]. Laccases, peroxidases and other oxygenases are also being studied for their abihty to degrade hazardous coal substances, especially the sulfur-containing components, and in the treatment of industrial waste and contaminated soil and water in the transformation of xenobiotics, polycycHc aromatic hydrocarbons and other pollutants (biodetoxification and biodecontamination)... 

As mentioned above, redox enzymes (oxidoreductases) are divided into four large groups dehydrogenases, oxygenases, oxidases, and peroxidases and catalases. 

Class 1. Oxidoreductases catalyze oxidation and reduction reactions. They include the dehydrogenases, oxidases, reductases, peroxidases, oxygenases, hydroxylases, and catalases. 

Figure 12 A diagram of the nitrogen cycle with catalyzing enzymes and metal requirements of each step. NIT, nitrogenase AMO, ammonium mono-oxygenase HAO, hydroxylamine oxidoreductase NAR, membrane-bound respiratory nitrate reductase NAP, periplasmic respiratory nitrate reductase NR, assimila-tory nitrate reductase NIR, respiratory nitrite reductase NiR, assimilatory nitrite reductase NOR, nitric oxide reductase N2OR, nitrous oxide reductase.

Fig. 1 The number of fold families identified from structural studies of proteins based on data obtained from SCOP. Representative structures are shown from each of the classes of protein fold, e.g., alpha or beta, that include enzymes. The proteins are represented as ribbons, colored from blue at the N-terminus through to red at the C-terminus. Cofactors and inhibitors are colored according to atom type and are represented in stick. For example, the alpha fold of Heme oxygenase is fold 143 out of 151 in the classification, a multihelical bundle containing two structural repeats of three-helical motif. The enzyme is an oxidoreductase EC 1.14.99.3 and is represented by the crystal structure of rat heme oxygenase-1 (HO-1) protein data bank acession code IDVG. (View this art in color at WWW. dekker. com.)...

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