Biology Reference
In-Depth Information
In the presence of VA or other high redox aromatic compounds, the cycle is
extended to a reacting Trp (Trp164 corresponding to P. chrysosporium Lip
H8 Trp171), which gives a neutral Trp-radical. Compound Ia is in equilibrium
with compound Ib containing iron in an oxyferryl form O
¼¼
Fe(IV) and a
Trp
.
). Compound Ib gives compound IIa
with the correlative oxidation of VA to radical-VA. Likewise, compound
IIa is in equilibrium with compound IIb containing iron in Fe
3
þ
form and the
Trp-radical. Compound IIb then yields the native form with the subsequent
oxidation of a second molecule of VA (
Ruiz-Duenas et al., 2007
).
Fe
4
þ
neutral Trp-radical (O
¼¼
4. Other peroxidases
Discovered in 1995 by screening dye-degrading microorganisms, the first dye
peroxidase (DyP) was purified and characterized from Thanatephorus cucu-
meris (formerly called Geotrichum candidum)cultures(
Kim et al., 1995
). Other
DyPs have since been found in several fungi and bacteria. DyPs are glycosy-
lated heme-peroxidases (9-31% glycosylation). These proteins are monomeric,
with a molecular mass ranging between 40 and 67 kDa and a pI between 3.5
and 4.3 (
Hofrichter et al., 2010
). They display several differences from the
'classical' peroxidases, such as a wide substrate specificity, and they are active
at lower pH than the other peroxidases. They show a weak sequence homology
with most other peroxidases such as LiPs andMnPs, as they do not contain the
conserved proximal and distal histidines and essential arginine found in other
plant peroxidase superfamily members (
Zubieta et al., 2007
).
A characteristic feature of all DyPs is their ability to oxidize synthetic high
redox potential dyes of the anthraquinone type, which can be oxidized only
with difficulty by other peroxidases (
Sugano et al., 2007
). Based on sequence
similarity, many more DyPs have recently been discovered in various organ-
isms, such as prokaryotes and archaea, and this family should be considered
as a novel class of peroxidases.
B. LACCASES
Laccases (p-diphenol:oxygen oxidoreductases, EC 1.10.3.2) were first discov-
ered in 1883, in the latex of the lacquer tree Rhus vernicifera (
Yoshida, 1883
).
The presence of laccases was identified in higher plants, insects, some bacte-
ria and in numerous fungal strains. Laccases are produced by deuteromy-
cetes, particularly Botrytis cinerea and Myceliophthora thermophila and by
ascomycetes such as Emericella (Aspergillus) nidulans and Neurospora crassa
(
Kurtz and Champe, 1982; Marbach et al., 1983
). However, the main produ-
cers are wood-rotting basidiomycetes. In the genus Pycnoporus, for example,
laccases are extracellular monomeric glycoproteins, and represent the only
