Copper amine oxidase enzyme

Although there are flavin-dependent as well as copper-dependent amine oxidases, this section will only deal with the copper enzymes. Amine oxidase (EC 1.4.3.6) catalyzes the oxidative reaction of amines to aldehydes and ammonia. The two-step process generates two electrons which are utilized to reduce oxygen to hydrogen peroxide (H202) [28,113] ... 

Amine oxidase catalyses the oxidative deamination of amines to the corresponding aldehyde, hydrogen peroxide and ammonia. The copper containing amine oxidase from pig plasma (PPAO) is one of the better characterised in this class of enzyme. The homogeneously pure enzyme has a molecular weight of 190,000 composed of two subunits with equal molecular weight. The present evidence suggests that copper is essential for catalytic activity and therefore much effort has been made to determine the structure of copper sites... 

Tropoelastin molecules are crosslinked in the extracellular space through the action of the copper-dependent amine oxidase, lysyl oxidase. Specific members of the lysyl oxidase-like family of enzymes are implicated in this process (Liu etal, 2004 Noblesse etal, 2004), although their direct roles are yet to be demonstrated enzymatically. Lysyl oxidase catalyzes the oxidative deamination of e-amino groups on lysine residues (Kagan and Sullivan, 1982) within tropoelastin to form the o-aminoadipic-6-semialdehyde, allysine (Kagan and Cai, 1995). The oxidation of lysine residues by lysyl oxidase is the only known posttranslational modification of tropoelastin. Allysine is the reactive precursor to a variety of inter- and intramolecular crosslinks found in elastin. These crosslinks are formed by nonenzymatic, spontaneous condensation of allysine with another allysine or unmodified lysyl residues. Crosslinking is essential for the structural integrity and function of elastin. Various crosslink types include the bifunctional crosslinks allysine-aldol and lysinonorleucine, the trifunctional crosslink merodes-mosine, and the tetrafunctional crosslinks desmosine and isodesmosine (Umeda etal, 2001). 

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). 

Copper-containing amine oxidases [E.C. 1.4.3.6] are one of the most widely distributed classes of Type 2 copper enzymes. They have been highly purified from bacteria. 

Other oxidoreductases that can play a major or less important role in drug metabolism are hemoglobin, monoamine oxidases (EC 1.4.3.4 MAO-A and MAO-B), which are essentially mitochondrial enzymes, the cytosolic molybdenum hydroxylases (xanthine oxidase, EC 1.1.3.22 xanthine dehydrogenase, EC 1.1.1.204 and aldehyde oxidase, EC 1.2.3.1), d the broad group of copper-containing amine oxidases (EC 1.4.3.6) (36-39). 

The copper-containing amine oxidases (copper amine oxidases, diamine oxidases) possess either a topaquinone or a 6-hydroxydopamine cofactor (Fig. 16.7-15), generally integrated in the oxidase primary structure. Tyrosine residues of the enzyme backbone in the active site are discussed as precursors for the prosthetic group[37]. 

Figure 12 Scheme of the current proposed mechanism for 2,4,5-trihydroxyphenylalanine quinone (TPQ) biogenesis in copper-containing amine oxidases. d02,ios represents the polypeptide of the enzyme, of which the precursor Tyr is part. R.D.S. is rate-determining step. Reproduced from B. J. Brazeau B. J. Johnson C. M. Wilmot, Biochem. Biophys. 2004, 428, 22-31, with permission from Elsevier Inc. 

Oxidative Deamination Reactions. The enzymes amine oxidases (AOs) catalyze the oxidative deamination of a wide range of biogenic amines. There are two classes of AOs copper AOs and flavin-containing AOs. Copper-containing AOs catalyze the oxidation of primary amines to aldehydes, with the subsequent release of ammonia and hydrogen peroxide, which requires one copper ion per subunit and topaquinone (TPQ) (2,4,5-trihydroxyphenylalanine) as cofactor (Figure 1.50). 

From the above studies it can be concluded that plant tissues contain a specific enzyme for the degradation of naturally occurring cytokinins having a A isopentenyl side chain. Mechanistically it would appear to be a copper-dependent amine oxidase. From the widespread occurrence of adenine and related compounds as metabolites of externally applied A isopentenyl cytokinins [8], it may be concluded that cytokinin oxidase is present in a large number of plant species. 

Copper Liver and organ meats grains, legumes, nuts, seeds (esp. cocoa powder) Component of many enzymes, especially oxidases Amine oxidases Lysyl oxidases Cytochrome oxidase... 

Copper is a component of many enzymes including amine oxidase, lysyl oxidase, ferroxidase, cytochrome oxidase, dopamine P-hydroxylase, superoxide dismutase and tyrosinase. This latter enzyme is present in melanocytes and is important in formation of melanin controlling the colour of skin, hair and eyes. Deficiency of tyrosinase in skin leads to albinism. Cu " ion plays an important role in collagen formation. 

So-called blue multinuclear copper oxidase enzymes, such as laccase and ascorbate oxidase, catalyze the stepwise oxidation of organic substrates (most likely in successive one-electron steps) in tandem with the four-electron reduction of O2 to water, i.e. no oxygen atom(s) from O2 are incorporated into the substrate (Eq. 4) [15]. Catechol oxidase, containing a type 3 center, mediates a two-electron substrate oxidation (o-diphenols to o-chinones), and turnover of two substrate molecules is coupled to the reduction of O2 to water [34,35]. The non-blue copper oxidases, e.g. galactose oxidase and amine oxidases [27,56-59], perform similar oxidation catalysis at a mononuclear type 2 Cu site, but H2O2 is produced from O2 instead of H2O, in a two-electron reduction. 

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