Bacterial Enzymes and Their Role in Decolorization of Azo Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 150

Cl

NaO N O

(a)

Cl

NADH + H + NADH + H +

NAD +

NAD +

Cl

NaO NH OH

Cl

(b)

Fig. 2 Reaction catalyzed by NADH-DCIP reductase. a Oxidized form of DCIP; b Reduced form
of DCIP

N

N

H

2 NADH + H +

2 NAD +

N

N

(a)

(b)

Fig. 3 Reaction catalyzed by MG reductase. a Malachite green; b Leucomalachite green

6.1.3 Lignin Peroxidase (LiP)

This enzyme belongs to the family of oxidoreductases, speci cally those acting on

peroxide as electron acceptor (peroxidases). The systematic name of this class
enzyme was 1,2-bis(3,4-dimethoxyphenyl) propane-1,3-diol:hydrogen-peroxide
oxidoreductase. LiP was N-glycosylated protein with molecular weight between 38
and 47 kDa. It contains heme in the active site and has shown a classical peroxidase
mechanism (Tien et al. 1986 ). LiP catalyzed several oxidation reactions in the side
chains of lignin and related compounds by one-electron abstraction to form reactive
radicals (Tien and Kirk 1983 ; Kersten et al. 1985 ). The cleavage of an aromatic ring
structure is also reported (Umezawa and Higuchi 1987 ). Several studies have found
a signicant induction in lignin peroxidase activity during decolorization of azo
dyes by bacterial strains, suggesting their possible function in dye decolorization.