Bacterial Enzymes and Their Role in Decolorization of Azo Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 151

OCH 3

OCH 3

OH

HO

OCH 3

H 2 O 2

OCH 3

HO

OH

+

H 3 CO

CHO

OCH 3

H 3 CO

OCH 3

(a) (b) (c)

Fig. 4 Reaction catalyzed by lignin peroxidase. a 1, 2-bis (3, 4-dimethoxyphenyl) propane-1,
3-diol; b 3, 4-dimethoxybenzaldehyde; c 1-(3, 4-dimethoxyphenyl) ethane-1,2-diol

The role of Lip in dye decolorizationwas proved by in vitro dye decolorization
assay with puri ed protein (Gomare et al. 2008 ). Reaction catalyzed by lignin

peroxidase is shown in Fig. 4 .

6.1.4 Laccase

Laccases (EC1.10.3.2) were mostly members of multi-copper oxidase protein
family. It was catalyzes the oxidation of substituted phenolic and non-phenolic
compounds in the presence of oxygen as an electron acceptor (Fig. 5 ). Phyloge-
netically, these enzymes have developed from small sized prokaryotic azurins
toeukaryotic plasma proteins ceruloplasmin (Claus 2003 , 2004 ). They contain four
histidine-rich copper binding domains, which coordinate types 1 3 copper atoms

that differ in their environment and spectroscopic properties (Givaudan et al. 1993 ).
They are classi

-

ed into two categories viz. blue laccase, had a blue color and
characteristic absorption and EPR spectra and white or yellow-brown laccase, had
no typical blue oxidase spectra and also showed atypical EPR spectra. According to
Solano and Sanchez-Amat ( 1999 ), a prokaryotic melanogenic marine bacterium
Marinomonas mediterranea containing two different polyphenol oxidases (PPO)
have characteristics of both tyrosinase and laccase activity. The other PPO is a
multi-potent enzyme, which is able to oxidize a wide range of substrate charac-
teristics for both tyrosinases and laccases. The reaction catalyzed by laccase
re

ected in Fig. 6 . The molecular weight of laccases varies from 60 to 390 kDa
(Call and Mucke 1997 ). First prokaryotic laccase was reported in rhizospheric
bacterium Azospirillum lipoferum (Solano et al. 1997 ). Laccase like activity has
been found also in Pseudomonas syringae and Pedomicrobium sp. (Ridge et al.
2007 ). Laccase was decolorized azo dyes by non-speci

c free radical mechanism,