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-
 
Search WWH ::




Custom Search