Molecular Plant Breeding 2016, Vol.7, No.9, 1-16
http:// mpb.biopublisher.ca
7
potential source of natural antioxidant products.
Superoxide dismutase has detoxifying capabilities
therefore fragment of gene that encodes two Mn-SODS
and Fe-SOD was detected in lettuce plant (Ruiz-Lozano
et al., (2001). Four types of Cu/Zn-SODs genes i.e.
SOD1, SOD4, SOD5 and SOD6 and two types of
Mn-SODs i.e. SOD2, SOD3 have been detected in C.
albicans (Martchenko et al., 2004). Superoxide
dismutases genes also have been found in human
pathogenic fungi like
C. neoformans
(Fang et al., 2002).
3.3 Catalase enzyme
Catalases (EC 1.11.1.6) are present in all those
organisms which are exposed to oxygen and catalyze
the decomposition of hydrogen peroxide (H2O2) into
water and oxygen (Chelikani et al., 2004). According to
Montavon et al., (2007) the conversion of H2O2 into
water and oxygen is necessary in living systems as
H2O2 is toxic to cells and the main site of H2O2
production is mitochondrion (Turrens, 2003).
In
textile industry catalase is used to remove H2O2 from
the fabrics (Goodsell, 2004) and in food industry this
enzyme is used to get rid of hydrogen peroxide from
food products (Chu et al., 1975). Catalase is a
and consisted of four polypeptide chains with more
than 500 amino acids (Boon et al., 2007). It has vital
role in reproductive reactions with highest turnover
number of all enzymes; just a single catalase molecule
can convert millions of H2O2 to water and oxygen in a
second (Goodsell, 2004). According to Zamocky et al.,
(2012) it is evident from phylogenetic analysis that the
corresponding genes are transferred during later steps
of
kat G
evolution through HGT (Horizontal Gene
Transfer) possibly from bacteriodetes to the ancestral
genome of fungi. Commercially, catalases are isolated
from mammalian liver and
A. niger
(Frost and Moss,
1987). In food and textile industries catalases are used
to remove hydrogen peroxide that is applied for
purpose of sterilization or bleaching (Akertek and
Tarhan, 1995). Catalase from Aspergillus is useful as it
is more resistant to heat (Nisshikawa et al., 1993).
Hydrogen peroxide is a strong nucleofilic oxidant
degraded by catalase and peroxidase synergistically to
protect the cells (Norton and Vuillemard, 1994). Fungi
are good producer of catalases as the fungal growth
take place in intimate contact with environment;
therefore catalases are continuously exposed and
affected by physical and chemical stress factors
(Kurakov et al., 2001). All aerobic organisms generate
reactive oxygen species, especially through aerobic
respiration, as a result of metabolic activity in fungi
reactive oxygen species (ROS) are formed and their
production increases due to different stress factors like
starvation, mechanical damage, light and interaction
with other living organisms (Loewen, 1997; Aguirre et
al., 2005). During the development of fungi regulation
of ROS level is very crucial (Gochev and Krastanov,
2007). As possessing mechanisms to adapt to
oxidative stress, fungi secrete SOD enzymes in the
extracellular space to minimize the negative impact of
reactive oxygen species (Tanaka and Izumitsu, 2010).
Catalases are regulated in different ways in bacteria,
plants and fungi (Ruis and Koller, 1997). These
enzymes are also concerned with development in
several organisms (Navarro et al., 1996). Cat-1 is
involved in conidia formation and is suitable for their
existence, as it shows a high resistance to high
temperature as well to many other denaturing
substances (Willekens et al., 1994). Catalases are
highly glycosylated enzymes and therefore are not
affected by H2O2 concentration (Diaz et al., 2001). In
the liquid medium activity of catalase is 60 times
higher in conidia as compared to growing hyphae
(Hansberg, 1996). Chary and Natvig, (1989) found
three distinct types of catalases in the life cycle of N.
crassa. The activity of catalase-3 was strong at the last
stage of exponential growth, while catalase-2 was
more active in aerial hyphae, and activity of
monofunctional cat-1 enhances several times during
conidia formation (Hansberg, 1996; Lledias et al.,
1999). The kinetic and molecular studies suggest that
cat-1 as well as other large catalases could tolerate
high concentrations of hydrogen peroxide (Lardinois
and Rouxhet, 1996), high thermoresistance (≥ 70°C)
(Switala et al., 1999) and enhanced resistance to
denaturants (Calera et al., 2000). Fungal catalases may
have specialized functions. Neurospora crassa has
three uncharacterized catalase genes (Chary and
Natvig, 1989) and only two have been characterized in
case of
A. nidulans
(Navarro and Aguirre, 1998)
.
In
N.
crassa,
catalases viz. CAT-1, CAT-2 and CAT-3 are
recognized to break H2O2 into water and oxygen. In
case of
A. niger
, extracellular catalase prevents cells
from H
2
O
2
(Witteveen et al., 1992). In A. nidulans two
differentially regulated genes Cat-A and Cat-B have
