Classes of Oxidizing Enzymes

Oxidative enzymes catalyze a very wide range of reactions, via a number of different mechanisms, and their nomenclature can at times be unclear in indicating their function, but several reviews are available to provide clarity [1-4]. The 

Multi-Step Enzyme Catalysis Biotransformations and Chemoenzymatic Synthesis Edited by Eduardo Garcia-Junceda 

Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31921-3 

The monooxygenase group of enzymes includes the non-P450 hydroxylases which catalyze the insertion of a hydroxyl group to replace a hydrogen atom at a saturated carbon [6-8] and the non-heme-dependent oxygenases such as the flavin-molybdenum-cobalt-dependent xanthine oxidase and aldehyde oxidase 

In flavin-dependent monooxygenases, a flavin-oxygen intermediate reacts with the substrate, also producing water in a second step, and requiring cofactors for regeneration of the flavin moiety. The unusual flavoprotein vanillyl-alcohol oxidase (EC 1.1.3.38), in which the flavin moiety is covalently bound, catalyzes the oxidation of p-substituted phenols as well as deamination, hydroxylation and dehydrogenation reactions [10]. 

---

Copper plays an important role in the constituents of many enzymes of the mammalian organism as well as in plants and anthropods. Several classes of oxidizing enzymes for copper have been described, including the cytochrome oxidases which are the terminal oxidases in the mitochondrial electron transport system, a key reaction in energy metabolism (34), and the amine oxidases (35) of which there are a number that contain copper (36,37,38), Lysyl oxidase (39) is probably the most important since it plays a major role in elastin and collagen synthesis... 

The electrons exchanged at each electrode need to be transported to the electrode to make the cell active. Redox enzymes are incapable of direct contact with the electrode since their redox centers are insulated from the con-duchve support by the protein matrices. In order to contact these enzymes with the electrode, mediators are utilized, which are dependent on the class of oxidative enzymes. 

In the field of enzymatic oxidations, especially the class of flavo enzymes with bound FAD as cofactor is interesting for synthetic applications. The... 

Alcohol dehydrogenases are a class of zinc enzymes, which catalyse the oxidation of primary and secondary alcohols to the corresponding aldehyde or ketone by the transfer of a hydride anion to NAD+ with release of a proton ... 

The marine environment acts as a sink for a large proportion of polyaromatic hydrocarbons (PAH) and these compounds have become a major area of interest in aquatic toxicology. Mixed function oxidases (MFO) are a class of microsomal enzymes involved in oxidative transformation, the primary biochemical process in hydrocarbon detoxification as well as mutagen-carcinogen activation (1,2). The reactions carried out by these enzymes are mediated by multiple forms of cytochrome P-450 which controls the substrate specificity of the system (3). One class of MFO, the aromatic hydrocarbon hydroxylases (AHH), has received considerable attention in relation to their role in hydrocarbon hydroxylation. AHH are found in various species of fish (4) and although limited data is available it appears that these enzymes may be present in a variety of aquatic animals (5,6,7,8). 

Dehydrogenases also represent a class of interesting enzymes since enantiose-lective reduction of ketones can lead to the production of enantiomerically pure secondary alcohols for the fine chemicals industry. Compared to liquid systems, in which the cofactor is often eliminated by the circulating phase in continuous systems, solid/gas catalysis can be highly suitable since it has been demonstrated that the cofactor is stable and its regeneration effective by addition of a second substrate. Also, stereoselective oxidation of secondary alcohols by these systems can help in the resolution of racemic mixtures. 

Another class of compounds that readily combine reversibly with molecular oxygen are the metal phthalocyanines.188,189 A number of oxidative enzymes contain the metal-porphyrin structure as the prosthetic group. In view of the... 

Apart from releasing photosynthetically reduced carbon and exporting elec-Irons, microbes also catalyze extracellular redox and hydrolysis reactions on I heir surfaces using external substrates. Of particular interest in our discussion is i class of surface enzymes in phytoplankton, deaminases, that catalyze the iclease of NII4 by oxidation of nitrogen containing compounds (Palcnik, 1989)... 

Clearly, most biocatalytic reactions for the production of fine chemicals are used to obtain enantiopure or enantioemiched compoimds, and only a minor nimiber of syntheses lead to products without chiral centers. More than 65 ap-pHcations of immobilized enzymes or whole cells for industrial research and production have been treated in this review, and it can be stated that approximately 80% utilize the class of hydrolytic enzymes. This number reflects the ease of handling and the broad utility of these enzymes. The reported hydrolytic enzyme applications mainly involve lipases, whereas other hydrolases can only be found in fewer but nevertheless just as attractive cases. The broad field of asymmetric synthesis (e.g., asymmetric reduction/oxidation) is defi-... 

Horseradish peroxidase is one of a class of heme enzymes (also including chloroperoxidase, vide supra) that catalyze the overall two electron oxidation of organic substrates with H2O2 as the oxidant or electron acceptor (Eq. 3) [50]. Unlike P-450 and chloroperoxidase, the axial fifth ligand to the heme iron of horseradish peroxidase is a nitrogen donor (histidine). 

As we have seen in chapters 1 and 2, the metabolism of arachidonate begins with its mobilization from membrane phospholipids and consists mainly of an array of sequential oxidative reactions. Three main classes of oxygenase enzymes are implicated prostaglandin H-synthase, also called cyclooxygenase cytochrome P450 and a variety of different lipoxygenases. 

---