Laccase LAC

Lac repressor 240 Laccase 887 Lactacystin 620, 620s Lactate 506s... 

There was no similar correlation between reactivity toward Fe(ll) and solvent exposure. FetSp and hCp exhibited similar rates of type 1 Cu(ll) reduction by Fe(ll) kohs > 1200s" ) while the rate with Co. cinereus Lac was >23s . In other words, laccases can use Fe(ll) as substrate but have no better than 1-2% of this activity in comparison to FetSp and hCp. In addition, they are at least 100-fold better than the ferroxidases in the turnover of bulky organic reductants. Combining the structure and reactivity features of these proteins indicates that the type 1 sites in the ferroxidases are less accessible to these large reductants and at the same time possess specificity elements that support the recognition and binding of Fe(II) as substrate. As outlined above, some of these elements may have been identified in hCp they remain uncharacterized in FetSp. 

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. 

Figure 9 The T1 Cu site in Tv lac with H-bonding to substrate analog, 2,5-xylindine (a) the overall substrate binding cavity is illustrated in (b) for and laccases. (Reprinted with permission from Ref 20. 2002 American Chemical Society)...

The mechanism of dioxygen reduction at the trinuclear cluster in MCO catalysis has been a strong focus for research on this class of copper oxidases. Dioxygen reduction has been most thoroughly investigated in Rhus laccase (a plant laccase, from the Japanese lacquer tree). The primary reason for using Rhus Lac is the availability of a metal-substituted form the enzyme, a TlHg form, in which the... 

Table V supplies insight into the relatedness within fungal laccases and ascorbate oxidases and to the other included proteins. Obviously both Tables Va and Vb show the same trend. The laccases of the narrowly related basiodomycetes P. radiata and C. hirsutus show differences of only 37%. The differences for the laccases from the ascomycetes N. crassa and C. parasitica are about 50%. The laccase of the deuteromy-cete A. nidulans shows very low identities to all partners of the alignment when all residues are included into the calculations (Table Va). The picture becomes clearer when badly aligning segments are omitted from the calculations (Table Vb). The differences from the other lac-...

FS Cfiakar, AJ Ragauskas. Tfie effects of oxidative aUcafine extraction stages after lac-case HBT and laccase NHAA treatments An NMR study of residual lignins. J Wood Chem Technol 20 169-184, 2000. 

Fig. 39 a, b. Phylogenetic trees of the structural domains of a laccase and ascorbate oxidase b ceruloplasmin. Plastocyanin is the reference protein in both cases. Lac/Aox 1-3 N- to C-ter-minal domains of laccase/ascorbate oxidase. Cpn 1-6 N- to C-terminal domains of ceruloplasmin. According to Ryden and Hunt 1993 [71]... 

The name laccase was first given to the enzyme by G. Bertrand (46) who studied its activity in crude form from the latex of the lac tree Rhus succedanea, and similar enzymes have been found in the latex of various other Asian lac trees... 

Laccase. A polyphenol oxidase has been purified from the sap of the lac tree by Keilin and Mann. Laccase differs from the potato and mushroom enzyme in several respects. With regard to substrate specificity, it oxidizes p-phenylenediamine more rapidly than catechol. p-Phenylene-diamine is not a substrate for the other polyphenol oxidases described. Laccase apparently is inert with p-cresol. It is not inhibited by carbon monoxide. Unlike the other phenol oxidases, this enzyme is not a pale yellow, but is blue, as is ascorbic acid oxidase (see below). This enzyme, however, is not an ascorbic acid oxidase. 

Plant phenolics of biphenyl type but of different biogenetic origin to those of the aucuparins are constituents of the sap of the lac tree (Rhus vernicifera, Anacardiaceae). The sap is the raw material of the Japan lacquer. It dries into a tough and brilliant film and has been used in the Orient as a coating material for thousands of years (75) (see also Chap. 1.1). The major constituent of the sap is urushiol (24). The drying process is believed to be an enzymatic oxidative coupling of urushiol under the influence of oxidoreductases - e.g. laccase to form biphenyls (e.g. 25), dibenzofurans (e.g. 26), oligomers, and polymers (88). 

Since the petroleum crises, all renewable natural resources have been intensively sought and studied to develop urgently needed materials for the future. Since Japanese lacquer will dry at room temperatures in the presence of laccase, this Japanese lac qjer is an energy conserving coating material, an excellent characteristic which may be added to its great durability. 

Also laccases, oxidoreductases with a Cu atom in the active center, have been successfully applied to the synthesis of phenol polymers. For example, phenol and several derivatives were polymerized by laccase from Pycnoporus coccineus (PCL) in aqueous organic solvents to yield the corresponding polymers [149]. The same enzyme was used to produce PPO from syringic acid (79) and from 2,6-dimethylphenol. Laccase from Myceliophthore (MPL) was found to catalyze the polymerization of syringic acid to PPO [135-137]. Lac-... 

The cathode enzyme laccase contains four copper ions, which are classified as three distinct types a type 1 (Lac-Tl), a type 2 (Lac-T2), and two type 3 (Lac-T3). The Lac-T2 and Lac-T3 pair is within 4 A of each other and forms a trinuclear cluster (Lac-T2/T3). The Lac-Tl copper is 13 A away from this cluster and serves as the site where electrons are accepted from the reducing substrate. Four electrons passing through the Lac-Tl site reduce all four copper ions, and the Lac-T2/T3 cluster then serves as the binding site for reduction of molecular oxygen to water. The somewhat complex reaction mechanism can be approximated as follows (Equations 9.2a-9.2d) (the charges of the copper sites are omitted for clarity) [3] ... 

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