Biology Reference
In-Depth Information
Native enzyme
A
×
-
3+
-
P
3+
-
P
O
2
-
Fe
Fe
×+
H
2
O
2
Ar
Compound III
H
2
O
Ar
×
+
4+
-
P
4+
-
P
O
K
Fe
O
K
Fe
×
+
Ar
Ar
Compound I
Compound II
Native enzyme
B
×
-
O
2
-
Fe
3+
-
P
3+
-
P
Fe
3+
H
2
O
2
Compound III
Mn
H
2
O
2+
Mn
4+
-
P
4+
-
P
+
O
K
Fe
O
K
Fe
3+
2+
Compound I
Compound II
Mn
Mn
VA
×
VA
C
Native enzyme
Compound IIb
3+
-
P
×
Fe
3+
-
Trp
Fe
3+
H
2
O
2
Mn
2+
H
2
O
Mn
4+
-
P
4+
-
P
+
O
K
Fe
O
K
Fe
3+
2+
Compound IIa
Mn
Mn
Compound Ia
VA
×
×
VA
4+
-
Trp
O
K
Fe
Compound Ib
Fig. 2. Mechanisms of lignin degradation by secreted heme-peroxidases: (A)
catalytic cycle of lignin peroxidase (LiP); (B) catalytic cycle of manganese peroxidase
(MnP); (C) catalytic cycle of versatile peroxidase (VP) sharing the characteristics of
both LiP and MnP.
to side-chain cleavage, demethylation, intramolecular addition and rearran-
gements. LiP-catalysed oxidation of phenolic compounds is typically asso-
ciated with a rapid fall in enzymatic activity (
Harvey and Palmer, 1990
). This
decrease is probably caused by the accumulation of the inactive LiP-III
during catalysis as phenoxy radicals are unable to reconvert LiP-III to the
native enzyme (
Chung and Aust, 1995
). LiPs are also capable of oxidizing
non-phenolic units of lignin by the formation of radical cations via one-