Multicopper oxidases laccases

Copper oxidases Blue oxidases (multicopper oxidases) Laccase Ascorbate oxidase Ceruloplasmin... 

The hemocyanlns which cooperatively bind dioxygen are found in two invertebrate phyla arthropod and mollusc. The mollusc hemocyanlns additionally exhibit catalase activity. Tyrosinase, which also reversibly binds dioxygen and dlsmutates peroxide, is a monooxygenase, using the dloxygen to hydroxylate monophenols to ortho-diphenols and to further oxidize this product to the quinone. Finally, the multicopper oxidases (laccase, ceruloplasmin and ascorbate oxidase) also contain coupled binuclear copper sites in combination with other copper centers and these catalyze the four electron reduction of dloxygen to water. 

The multicopper oxidases (laccase, ascorbate oxidase, and ceruloplasmin) catalyze a four-electron reduction of dioxygen to water (285-287). Consistent with the four-electron stoichiometry, the enzymes contain four copper ions. One of the copper ions is type I, causing an intensely blue color of the proteins, thus the enzymes of this family are referred to as blue oxidases. They also contain a monomeric copper site that exhibits normal spectroscopic features, whereas the other two copper... 

Guss et al., 1992 Romero et at., 1994). In stellacyanin, a glutamine Os fulfills this role (Hart et al., 1996 Vila and Fernandez, 1996). In azurin, in addition to the axial methionine, a peptide carhonyl of a glycine acts as weak axial hgand located on the opposite side to Met (Baker et al., 1988 Nar et al., 1991) (Fig. 2). The multicopper oxidase laccase possesses a trigonal Type I site, with no axial hgand (Ducros et al., 1998). However, no NMR studies are available for any protein of the latter class and they are not considered further here. 

A new effective photocatalyst has been obtained by association of the Zn-tetramethylpyridinium porphyrin photosensitizer with multicopper oxidase laccase. This system merges the oxidation of an electron donor [i.e. an organic molecule) with the four-electron reduction of diojygen to water, thus realising the idea of photo-driven transformations on substrates using enzyme-photosensitizer hybrids. ... 

Quintanar L, Yoon J, Aznar CP, Palmer AE, Andersson KK, Britt RD, Solomon El. 2005. Spectroscopic and electronic structure studies of the trinuclear Cu cluster active site of the multicopper oxidase laccase nature of its coordination unsaturation. J Am Chem Soc 127 13832-13845. 

Brown MA, Zhao Z, Grant Mauk A. Expression and characterization of arecombinant multicopper oxidase laccase IV from Trametes versicolor. Inorg Chim Acta 2002 331 232-238. 

Blue Multicopper Oxidases. These include laccases, ascorbate oxidase, and ceruloplasmin [22,61], which along with cytochrome c oxidase (CcO with Fe and Cu) can couple the one-electron oxidation of substrates (e.g., ascorbate, diamines, monophenols Fe2+ for ceruloplasmin cytochrome c, for CcO) to the full reduction of dioxygen to water (i.e., 02 + 4c + H+ —> 2H20). 

Some proteins contain more than one copper site, and are therefore among the most complicated and least understood of all. The active site known as type 4 is usually composed of a type 2 and a type 3 active site, together forming a trinuclear cluster. In some cases, such proteins also contain at least one type 1 site and are in this case termed multicopper oxidases, or blue oxidases [3], Representatives of this class are laccase (polyphenol oxidase) [7-9], ascorbate oxidase (Figure 5.Id) [10], and ceruloplasmin [11], which catalyze a range of organic oxidation reactions. 

AO = Ascorbate oxidase (h)Cp = (human) Ceruloplasmin CT = Charge transfer Hp = Hephaestin GPl = Glycosyl-phosphatidylinositol Lac = Laccase MCO = Multicopper oxidase T1(2,3)D = Type 1 depleted (and/or type 2 or type 3) Tf = Transferrin. 

Ascorbate oxidase, laccase, and ceruloplasmin form the group of blue oxidases. These are multicopper enzymes catalyzing the four-electron reduction of dioxygen to water with concomitant one-electron oxidation of the substrate (3), which is very similar to the reaction performed by cytochrome c oxidase. All three enzymes have been known for many years, and an overwhelming number of papers have appeared since their discovery dealing with the different aspects of these enzymes. 

The high-affinity pathway involves oxidation of Fe to Fe by the ferroxidase FET3 and subsequent transport of Fe " " across the plasma membrane by the permease FTRl. FET3p is a member of the family of multicopper oxidases, which include ascorbate oxidase, laccase, and ceruloplasmin (see Chapter 14), and does not become functional until it is loaded with copper intracellularly through the activities of the copper chaperone ATX Ip and the copper transporter CCC2p. It appears that Fe " " produced by FET3 is transferred directly to FTRl, and does not equilibrate with the bulk phase, as is illustrated in Fig. 7.13. This is almost certainly achieved by the classic metabolite-channeling mechanism, a common feature of multifunctional enzymes. 

Laccase, ascorbate oxidase, and ceruloplasmin are the classical members of the multicopper oxidase family also known as blue oxidases. Recently, a small number of bacterial members of this family have been characterized, including CueO from E. coli a spore-coat laccase (CotA) from Bacillus suhtilis and phenoxazinone synthase from Streptomyces antibioticus The catalyzed reaction of these enzymes except for phenoxazinone synthase is given in Equation (11). A comprehensive overview of the broad and active research on blue copper oxidases is presented in Messerschmidt. Recent results have been included in a review on the reduction of dioxygen by copper-containing enzymes. The nature and number of the different copper sites in blue oxidases has been described in the sections about the type-1 copper site and the trinuclear copper cluster. 

Figure 4-3 Homology between Fet3p and the multicopper oxidases. Comparison was done using the ClustalW alignment program. Underlined sequence represents multicopper oxidase domains. Bold sequences represent hydrophobic regions. Only one representative member of each family was used in the comparison. Laccase is from Thanatephorus cucunteris, Ctenbank accession number 2833189. AO is an ascorbate oxidase from Cucumis sativus (cucumber), Genbank accession number 114270. PCOA is the copper resistance protein PCOA from...

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