Biology Reference
In-Depth Information
External Trp
Fig. 4. Structure of versatile peroxidase (PDB
2BOQ
;
Perez-Boada et al., 2005
)
showing the external Trp involved in long-range electron transfer towards heme and
the two structural calcium ions found in all peroxidases.
enzyme surface, and electrons are transferred to the heme by a protein
pathway (
Martinez et al., 2005
).
VPs share properties of both LiPs and MnPs, and are able to oxidize their
respective substrates. Thus, VPs are able to oxidize Mn
2
þ
to Mn
3
þ
like MnPs,
as well as to degrade non-phenolic lignin units or VA Mn-independently, like
LiPs. However, the affinity of VPs for these substrates is lower than that of LiPs
(
Higuchi, 2004
). In addition, VPs are able to oxidize hydroquinones and sub-
stituted phenols directly, whereas these compounds are not efficiently oxidized
by LiPs or MnPs, when VA or Mn
2
þ
are respectively lacking. The oxidation of
dyes with high redox potentials such as Reactive Black 5 is also possible in the
presence of VA. The optimal pH of VPs for Mn
2
þ
oxidation is around 5 when
optimum oxidation of aromatic compounds occurs at pH 3. These values are
close to the optimal pH for MnPs and LiPs, respectively (
Martinez, 2002
).
Owing to their high affinity for Mn
2
þ
, VPs were initially described as
'peroxidases oxidizing Mn
2
þ
exhibiting Mn-independent activity'. However,
a more thorough characterization of their kinetic properties suggests an
effective oxidation and even a higher affinity for certain aromatic substrates
and dyes compared with LiPs and MnPs (
Heinfling et al., 1998a,b,c
).
The basic catalytic cycle of VPs (
Fig. 2
C) is similar to those of other
peroxidases with the two intermediary compounds I and II, but is more
complex due to a more diversified pool of potential substrates. The first
step is the oxidation of native enzyme (Fe(III)
P) by hydrogen peroxide
P
.
þ
). This compound undergoes a first
reduction with the oxidation of Mn
2
þ
to yield compound IIa (O
Fe
4
þ
to give compound Ia (O
¼¼
Fe
4
þ
P),
followed by a second monoelectronic reduction to return to the native form.
¼¼
