V
and temperature when ABTS was used as substrate. ABTS was the best substrate tested for
En3-Lac-2 and En3-Lac-3, but En3-Lac-4 showed the highest affinity to DMP. En3-Lac-2
showed stronger pH stability and thermostability. En3-Lac-2 also had a stronger ability to
tolerate metal ions and organic solvents compared with other two isoenzymes.
Different laccase isoenzymes purified from Ganoderma sp.En3 were used to degrade
different types of synthetic dyes. The degradation ability of these laccase isoenzymes was
different. There existed distinct substrate specificity among these isoenzymes. Different
laccase isoenzymes had different decolorization capabilities. En3-Lac-2 had a stronger
capability for decolorizing the triphenylmethane and indigo dye, while En3-Lac-4 had a
stronger ability to decolorize the azo and anthraquinone dye. En3-Lac-3 showed the
weakest decolorization ability, which could only degrade MG. The kinetic study on the
decolorization ability of each isoenzyme indicated that there existed a distinct difference
on the substrate specificity among these enzymes. En3-Lac-2 catalyzed the decolorization
of IC with the highest efficiency (K
cat
=4.03 s
-1
), while MG for En3-Lac-3 (K
cat
=2.58 s
-1
)
and RBBR for En3-Lac-4 (K
cat
=1.26 s
-1
). En3-Lac-4 had the largest range of substrates,
which could efficiently degrade all the dyes except AF and RB5. In order to promote the
decolorization efficiency of laccases, the effect of different mediators on the degradation
of AF by En3-Lac-4 was studied and the decolorization efficiency was increased 118-fold
by the mediator syringaldehyde. The differences in decolorization capability of laccase
isoenzymes were eliminated after adding the mediator syringaldehyde.
Among the three laccase isoenzymes purified in our research, En3-Lac-3 had the
weakest degradation ability, but there existed a positive synergistic effect of different
laccase isoenzymes on the decolorization capability. Combination of En3-Lac-3 with other
two isoenzymes greatly promoted the decolorization of different azo dyes. The synergistic
effect was related to the rate of different isoenzymes, and the addition of En3-Lac-3 could
promote the degradation of azo dyes by En3-Lac-4 more effectively.
Furthermore, we evaluated the degradation of different PAHs by these laccase
isoenzymes. En3-Lac-3 and En3-Lac-4 could efficiently degrade all the PAHs selected in
our research, more specifically, Anthracene (Ant), Fluoranthene (Fla), Fluorene (Flu),
Phenanthren (Phe) and Pyrene (Pyr), with a degradation efficiency higher than 85% in 24h.
However, the degradation ability of En3-Lac-2 was relatively weak. It could barely
degrade Pyr (less than 10% in 24h). The degradation reactions of PAHs by all the three
