Blue multicopper oxidase

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). 

The blue multicopper oxidases couple the oxidation of substrates to the four-electron reduction of molecular oxygen to In this respect they... 

Although remarkable, neither of the systems reviewed in this last section has direct bearing or closely resembles the native intermediate of the laccase. Modeling of blue multicopper oxidase O2 binding, O—O reductive cleavage, and fully understanding the role of protons and protonation levels remain a challenging research areas for the future. 

The blue multicopper oxidases constitute a heterogeneous family of enzymes from different sources (7). In addition to the well characterized members of this family, ascorbate oxidase (45,46), laccase (47,48), and ceruloplasmin (49,50), all from higher organisms, two other proteins have attracted much recent interest FetSp, which is involved in iron uptake in yeast (51), and CueO, which is required for copper homeostasis in Escherichia coli (52). The characteristic reactivity of these enzymes is the one-electron oxidation of four substrate equivalents coupled to the four-electron reduction of dioxygen to water (1). These processes occur at a catalytic unit constituted by four copper atoms classified according to their spectroscopic properties in... 

Largely due to the great difficulty associated with obtaining quantities of purified enzyme adequate for physical-chemical studies its characterization has not been carried to the same stage as that of ceruloplasmin and the laccases. Nevertheless, recent developments in the purification procedure (191, 192) have allowed measurements which signify a great similarity of the Cu-binding sites on this enzyme with those of other blue, multicopper oxidases. The properties of the enzyme are summarized in Table 2. 

Cu nitrite reductase The Cu-dependent nitrite reductase, which transforms nitrite to nitric oxide in denitrifying bacteria, contains both the type-1 and the type-2 Cu center but lacks the binuclear type-3 site [89]. Yet, its arrangement of Cu atoms within the protein indicates a strong structural relationship with the classical blue multicopper oxidases [85], It catalyzes the single-electron reduction of NO2 to NO and water [Eqs. (5)-(7)] ... 

Blue multicopper oxidases (BMCOs) such as laccase, ceruloplasmin, bilirubin oxidase (BOx), and ascorbate oxidase (AOx) have been extensively investigated as cathodic biocatalysts for DET-based biodevices [44]. BMCOs have a catalytic center consisting of four coppers a type 1 (Tl) Cu site, which accepts electrons from the substrate and from the electrode surface, and a type 2/type 3 (T2/T3) cluster, where O2 is reduced directly to water. High redox potential laccases and BOx, with redox potential up to 780 and 670 mV versus normal hydrogen electrode (NHE), respectively [44,45], can be used to create efficient biocathodes with current densities up to a few mA cm . In 2012, Shleev and coworkers used the DET ability of these enzymes to create several completely DET-based BFCs [42]. The enzymes have also been used in different MET-based approaches [46,47] specifically, Heller and coworkers... 

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

Laccase is perhaps the metallo-enzyme most widely used for this aim. Laccases are a family of multicopper ( blue copper ) oxidases widely distributed in nature Many laccases have fungal origin, while others are produced in plants. They contain four Cu(II) ions, and catalyse the one-electron oxidation of four molecules of a reducing substrate with the concomitant four-electron reduction of oxygen to water . In view of their low redox potential, which is in the range of 0.5-0.8 V vs. NHE depending on the fungal source laccases typically oxidize phenols (phenoloxidase activity) or anilines. 

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. 

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... 

Multicopper Oxidases Type 1 (Blue) Type 2 (Normal) Type 3 (Coupled Binuclear) Total Cu... 

This research was supported by the National Science Foundation (CHE-9217628) for the blue copper studies and by the National Institutes of Health (DK-31450) for the coupled binuclear and multicopper oxidase studies. Edward I. Solomon expresses his sincere appreciation to all his students and collaborators who are listed as co-authors in the references for their commitment and contributions to this science. 

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. 

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