Environmental Engineering Reference
In-Depth Information
many researchers who investigated fungal dye decolorization also mea-
sured the activities of those ligninolytic enzymes to explore the dye decol-
orization mechanisms. Table 6.2 summarizes such studies. It is interesting
to note that many of these studies (except for the earlier studies such as
Bumpus and Brock [22]) suggested the importance of laccase, MnP, and
manganese-independent peroxidase in dye decolorization, while LiP
appeared to be less important. The involvement of so-called Remazol
Brilliant Blue R (RBBR) oxidase in dye decolorization by certain white
rot fungi has been suggested [63]. Because of the requirement of hydro-
gen peroxide in the catalysis of peroxidase enzymes, hydrogen peroxide-
producing oxidases such as aryl-alcohol oxidase and glyoxal oxidase are
also important in the fungal decolorization [14,46].
6.5
Classification and Enzymology of
Ligninolytic Enzymes
This section briefly describes the classification and enzymology of impor-
tant ligninolytic enzymes that have been studied for dye decolorization.
Those enzymes include LiP, MnP, versatile peroxidase, DyP, and laccase.
More detailed literature reviews on the structure, functions, and produc-
tion of these enzymes can be found elsewhere [16,27,38,97].
6.5.1 Peroxidases
Peroxidases are a group of oxidoreductases that catalyze the reduction of
peroxide such as hydrogen peroxide to water and the oxidation of a vari-
ety of organic and inorganic compounds [98]. The term peroxidase repre-
sents a group of specific enzymes such as NADH peroxidase (EC 1.11.1.1)
and glutathione peroxidase (EC 1.11.1.9), and iodide peroxidase (EC
1.11.1.8), as well as a group of nonspecific enzymes. Currently, there are
13 major groups of peroxidase enzymes that can be subdivided into more
than 60 classes, according to PeroxiBase (http://peroxibase.toulouse.inra.
fr/index.php).
The general catalytic cycle of peroxidases can be described as follows
[99,100]:
Resting State + H
2
O
2
Compound I + H
2
O
(6.1)
Compound I + AH
2
Compound II + AH·
(6.2)
Compound II + AH
2
resting state + AH· + H
2
O
(6.3)
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