Lysine oxidase function

RuBisCO is constituted of a large and a small subunit, and performs both the carboxylation at C2 of ribulose and its oxidation at the same site with 50% selectivity [55]. The mechanism of action is quite complex - it has been shown that for both carboxylase and oxidase functions RuBisCO has an active site constituted by a lysine residue and a catalytic site, both placed in the large subunit Once the two C3 moieties are formed (Scheme 1.3 c) the carboxyhc functionalities are reduced and the two C3 moieties coupled to afford glucose. Formally the process consists of a CO2 reduction to a HCOH moiety, inserted into a C-C bond of a C5 sugar to afford a C6 compound. This process uses some tens of gigatons per year of carbon of CO2 in the natural carbon cycle. 

Peptidyl hydroxyprohne and hydroxylysine are formed by hydroxylation of peptidyl proline or lysine in reactions catalyzed by mixed-function oxidases that require vitamin C as cofactor. The nutritional disease scurvy reflects impaired hydroxylation due to a deficiency of vitamin C. 

After secretion from the cell, certain lysyl residues of tropoelastin are oxidatively deaminated to aldehydes by lysyl oxidase, the same enzyme involved in this process in collagen. However, the major cross-links formed in elastin are the desmosines, which result from the condensation of three of these lysine-derived aldehydes with an unmodified lysine to form a tetrafunctional cross-hnk unique to elastin. Once cross-linked in its mature, extracellular form, elastin is highly insoluble and extremely stable and has a very low turnover rate. Elastin exhibits a variety of random coil conformations that permit the protein to stretch and subsequently recoil during the performance of its physiologic functions. 

The storage role of (Cu,Zn)-SOD in seeds e.g. seems plausible, when the Cu-carrier function of ceruloplasmin is considered The lipophilic anti-inflammatory and anti-ulcer Cu-chelates could also raise the Cu concentration in certain tissues and thus enhance their lysyl oxidase activity. But especially Cu(acetylsalicylate)2 inhibited protine,2-oxoglutarate dioxygenase (EC 1.14.11.2) and lysine,2-oxoglutarate dioxygenase (EC 1.14.1.4), which are also important enzymes in the processing of collagen... 

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). 

Lysyl oxidases catalyze the oxidation of the e-amino group in the side chain of lysine residues in proteins, producing a reactive aldehyde functional group, which can form Schiff-base adducts with unmodified lysine residues or undergo aldol addition, creating covalent cross-links between polypeptide chains. " Lysyl oxidases are widespread in nature, and have been isolated from organisms ranging from yeast to man. 

Dbpner, S., Hildebrandt, P., Resell, E.L, Mauk, A.G., Walter, M.V., Buse, G., and Soulimane, T. (1999) The structural and functional role of lysine residues in the binding domain of cytochrome c in the electron transfer to cytochrome c oxidase. European Journal of Biochemistry, 261, 379-391. 

Another type of inportant structural ECM proteins, the elastin, is rich in elastic tissues and organs, such as the cardiovascular and pulmonary system and skin, and of extreme importance for their proper function. The precursors of native elastin, the tropoelastins, are composed of alternating hydrophobic domains, enabling hydrophobic interaction, and lysine-rich domains, allowing for covalent cross-linking through the mediation of the enzyme lysyl oxidase. 

A brief discussion of the chemical reactivity of the products of these enzymes is central to our proposed use of these enz)nnes as antinutritive bases of resistance. Polyphenol oxidase (PPO) and peroxidase (POD) oxidize phenolics to quinones, which are strong electrophiles that alkylate nucleophilic functional groups of protein, peptides, and amino acids (e.g., -SH, -NHof -HN-, and -OH)(Figure 1)(53,63-65). This alkylation renders the derivatized amino acids nutritionally inert, often reduces the digestibility of protein by tryptic and chymotryptic enzymes, and furthermore can lead to loss of nutritional value of protein via polymerization and subsequent denaturation and precipitation (63,66-69). POD is also capable of decarboxylating and deaminating free and bound amino acids to aldehydes (e.g., lysine, valine, phenylalanine. 

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