Oxidative enzymes, classification

Many papers have been published about the enzymatic degradation of polyphenols through the action of oxidizing enzymes. Thus, various classifications have been provided for these types of biocatalytic molecules, according to their coenzyme requirements or according to the nature of the oxidizing substrate (the electron acceptor) and the reaction products (Fig. 4.1). 

The use of enzymes and whole cells as catalysts in organic chemistry is described. Emphasis is put on the chemical reactions and the importance of providing enantiopure synthons. In particular kinetics of resolution is in focus. Among the topics covered are enzyme classification, structure and mechanism of action of enzymes. Examples are given on the use of hydrolytic enzymes such as esterases, proteases, lipases, epoxide hydrolases, acylases and amidases both in aqueous and low-water media. Reductions and oxidations are treated both using whole cells and pure enzymes. Moreover, use of enzymes in sngar chemistiy and to prodnce amino acids and peptides are discnssed. 

One of the most attractive analyte for amperometric enzyme electrodes is blood glucose. The specifier of choice is the enzyme glucose oxidase (EC 1.1.3.4, Enzyme Classification acc. to Enzyme Nomenclature of the lUB) catalyzing the oxidation of glucose to gluconolactone. The oxidation takes place in two steps ... 

CAS 9001-05-2 EINECS/ELINCS 232-577-1 Classification Oxidizing enzyme Definition Enzyme found in animals, plants, bacteria, and fungi... 

Although the term monoamine oxidase suggests a single enzyme species, it is now apparent that there are a variety of enzymes which oxidatively deaminate amines. The classification into diamine oxidase and MAO is also not absolute since MAO will metabolize diamines including histamine (Fonts et al., 1957). Amine-oxidizing enzymes are also present in the blood of certain species (Tabor et al., 1954 Blaschko et al., 1958). These enzymes are not like the mitochondrial MAO. It may well be that there are a large number of amine oxidases, some of which are fairly specific for a given amine and others quite nonspecific. A similar situation exists with respect to cholinesterase activity. 

An excellent classification of this type of enzymes was that of Burton (2003). Because of their importance in polyphenol degradation, we have studied four enzymes closely related with the oxidation of phenolic compounds polyphenoloxidase, peroxidase, laccase, and lipoxygenase. 

Amine oxidases catalyze the oxidation of amines, diamines, and polyamines. According to their ability to recognize one of those substrates preferentially, amine oxidases may be divided into monoamine oxidases, diamine oxidases, and polyamine oxidases, respectively. Several different enzymes fall into the amine oxidase class, and the classification of some of them still remains ambiguous. The term monoamine oxidase (flavin-containing, EC 1.4.3.4) was introduced to contrast with copper-containing amine oxidases (EC 1.4.3.6). 

The location, structure, classification, regulation, and mechanism of action of CYPs are discussed in Chapter 9. This chapter summarizes the reactions involved in the oxidation of xenobiotics by CYP and other enzymes. Although microsomal monooxygenase reactions are basically similar with respect to the role played by molecular oxygen and in the supply of electrons, the enzymes are markedly nonspecific, with both substrates and products falling into many different chemical classes. It is convenient, therefore, to classify these activities on the basis of chemical reactions, bearing in mind that not only do the classes often overlap, but the same substrate may undergo more than one oxidative reaction. 

Oxidoreductases play a central role in the metabolism and energy conversion of living cells. About 25% of the presently known enzymes are oxido reductases [104]. The classification of oxidoreductases is presented in Fig. 3.38. The groups of oxidases, monooxygenases and peroxidases - dealing with oxidations - will be described in Chapter 4. 

Oxidations by enzymes are performed by the group of oxidoreductases. An overview of the classification of oxidoreductases is given in Fig. 4.11. 

The organophosphorus insecticides are all structurally related and undergo similar reactions. The chemical classification of the most widely used compounds of this type is given in Table V. These compounds can also be differentiated on the basis of whether they are largely effective per se or undergo oxidative conversions in plants or animals. All are inhibitors of the enzyme, cholinesterase. Their potency depends not only upon their intrinsic enzyme affinity but also on anticholinesterase properties acquired through in vivo metabolism. 

Figure 1 Classification of Mo-MPT enzymes. Structures (l)-(3) represent oxidized active-site structures (only the dithiolene moiety of each MPT-based ligand is shown)...

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