Use of Fungal Laccases and Peroxidases for Enzymatic Treatment of Wastewater Containing Synthetic Dyes - Green Chemistry for Dyes Removal from Wastewater - page 227

a plant pathogenic Basidiomycota Thanatephorus cucumeris Dec 1 [117].
Interestingly, this T. cucumeris Dec 1 was later found to be a white rot fungus
B. adusta . Although this enzyme was first considered as a class II (fungal)
peroxidase because of its origin, the primary structure of the cloned DyP
was significantly different from those of other class II peroxidases such as
LiP and MnP and those of non-animal peroxidases. Currently, DyP is clas-
sified as a member of a separate peroxidase group under heme peroxidase
called the DyP-type peroxidase family [98]. DyP also differs from versatile
peroxidase because the former enzyme exhibited higher decolorization
activities toward anthraquinone dyes such as Reactive Blue 5 than toward
azo dyes. In addition to the typical peroxidase reactions, the DyP from
B. adusta can catalyze the hydrolysis of anthraquinone rings [118,119].
The reported exceptional ability of B. adusta and other Bjerkandera spe-
cies on dye decolorization may be due to this DyP enzyme. It is unclear if
the previously described high-performance “hybrid” MnP from B. adusta
[36,116,120] is identical to DyP.
The published crystal structures of versatile peroxidase from P. eryngii
[121] and DyP from B. adusta [77] are shown in Figure 6.12.
6.5.2 FungalLaccases
Laccases ( p -diphenol:dioxygen oxidoreductase; EC 1.10.3.2) are copper-
containing oxidase enzymes and one of two groups of oxidase enzymes
called polyphenol oxidases [122]. Laccases are widely distributed in plant,
fungi, and other microorganisms. In particular, laccasses are ubiquitous
in fungi and have been detected and purified from many species such as
white rot fungus T. versicolor , edible mushroom Agaricus bisporus , and
Ascomycota Neurospora crassa [16,26,123]. Diphenols such as hydroqui-
none and catechol are the major substrates of laccases and are oxidized to
free radicals by a one-electron reaction catalyzed by laccases. The initial
product is usually unstable and may either undergo a second oxidation to
quinones or undergo non-enzymatic reactions such as disproportionation
and/or polymerization, giving an amorphous insoluble melanin-like prod-
uct [26]. Laccases are also known to catalyze the oxidation of a range of
substituted monophenols, polyphenols, and other aromatic compounds,
resulting in demethylation, polymerization and depolymerization of the
substrates. A crystal structure of laccase from T. versicolor [124] is shown
in Figure 6.13.
Although the contribution of laccases to lignin degradation by white
rot fungi such as T. versicolor has been speculated, its true role in ligni-
nolysis was less clear than those of LiP and MnP, partly because the low