2.8.1 Oxidoreductases
Oxidoreductases are a broad group of enzymes that catalyze the transfer of electrons
from one molecule (redundant or electron donor) to another (oxidant or electron
acceptor). Most of these enzymes require additional cofactors to function as electron
donors, electron acceptors, or both. These enzymes have applications in bioremediation, during which they catalyze the oxidation/reduction reaction by electronically
incorporating molecular oxygen (O 2 ). In these reactions, oxygen is reduced to water
(H 2 O) or hydrogen peroxide (H 2 O 2 ).
A fungus Cladosporium cladosporioides was isolated from organophosphate
contaminated soil, which showed the potential to use chlorpyrifos as the sole carbon
source (Gao et al. 2012). The parent chlorpyrifos was first produced by hydrolysis of
3,5,6-trichloro-2 pyridinol (TCP) and diethylthiophosphoric acid (DETP). The
hydrolysis product is further transformed by the breakage of the TCP ring, resulting
in its complete detoxification (Chen et al. 2012). Likewise, Lu et al. (2013) isolated a
bacterial strain called Cupriavidus spp. DT-1 responsible for the degradation of
chlorpyrifos. In the degradation path, chlorpyrifos was first hydrolyzed to TCP,
dechlorinated to 2-pyridinol, respectively, and then to the cleavage of the pyridine
ring and further degradation. The mpd gene, which encodes the enzyme responsible
for chlorpyrifos hydrolysis to TCP, was cloned and expressed in Escherichia coli
BL21. Inoculation of chlorpyrifos-contaminated soil with strain DT-1 reduced
chlorpyrifos and TCP at 100% and 94.3%, compared to 28.2% and 19.9% in
uninoculated soil, respectively.
Oxidases constitute a subclass of oxidoreductase enzymes (Scott et al. 2008). The
products of oxidation reactions often contain anionic hydroxyl or carboxyl substituents and are more polar and water soluble than parent pesticides. Glyphosate
oxidase (GOX) is the best characterized oxidase involved in pesticide bioremediation (Scott et al. 2008). Most of the chloroaromatics molecules are converted by
bacteria to chlorocatechol or chloroprotocatechuate, which become the starting
substrate for subsequent reactions involving oxidative cleavage. Monooxygenases
metabolize the xenobiotics by often enhancing their reactivity and/or the water
solubility through the addition of oxygen atom. A two-component flavin diffusible
monooxygenase family (TC-FDM) (Galan et al. 2000) is a monooxygenase that
plays a role in the degradation of environmental pesticide residues. The cytochrome
P450 family is another large group of monooxygenase enzymes that have a wide
substrate range and have been reported to catalyze biochemically recalcitrant
reactions, such as oxidation or hydroxylation of non-activated carbon atoms
(Werck-Reichhart et al. 2000). An example of the use of cytochrome P450 in the
bioremediation of herbicides is cytochrome CYP1A1 (also known as aryl hydrocarbon hydroxylase) from mammalian liver, which has been found to degrade atrazine,
norflurazon and chlortoluron (Kawahigashi et al. 2005).
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A. Sehrawat et al.
Oxidoreductases are a broad group of enzymes that catalyze the transfer of electrons
from one molecule (redundant or electron donor) to another (oxidant or electron
acceptor). Most of these enzymes require additional cofactors to function as electron
donors, electron acceptors, or both. These enzymes have applications in bioremediation, during which they catalyze the oxidation/reduction reaction by electronically
incorporating molecular oxygen (O 2 ). In these reactions, oxygen is reduced to water
(H 2 O) or hydrogen peroxide (H 2 O 2 ).
A fungus Cladosporium cladosporioides was isolated from organophosphate
contaminated soil, which showed the potential to use chlorpyrifos as the sole carbon
source (Gao et al. 2012). The parent chlorpyrifos was first produced by hydrolysis of
3,5,6-trichloro-2 pyridinol (TCP) and diethylthiophosphoric acid (DETP). The
hydrolysis product is further transformed by the breakage of the TCP ring, resulting
in its complete detoxification (Chen et al. 2012). Likewise, Lu et al. (2013) isolated a
bacterial strain called Cupriavidus spp. DT-1 responsible for the degradation of
chlorpyrifos. In the degradation path, chlorpyrifos was first hydrolyzed to TCP,
dechlorinated to 2-pyridinol, respectively, and then to the cleavage of the pyridine
ring and further degradation. The mpd gene, which encodes the enzyme responsible
for chlorpyrifos hydrolysis to TCP, was cloned and expressed in Escherichia coli
BL21. Inoculation of chlorpyrifos-contaminated soil with strain DT-1 reduced
chlorpyrifos and TCP at 100% and 94.3%, compared to 28.2% and 19.9% in
uninoculated soil, respectively.
Oxidases constitute a subclass of oxidoreductase enzymes (Scott et al. 2008). The
products of oxidation reactions often contain anionic hydroxyl or carboxyl substituents and are more polar and water soluble than parent pesticides. Glyphosate
oxidase (GOX) is the best characterized oxidase involved in pesticide bioremediation (Scott et al. 2008). Most of the chloroaromatics molecules are converted by
bacteria to chlorocatechol or chloroprotocatechuate, which become the starting
substrate for subsequent reactions involving oxidative cleavage. Monooxygenases
metabolize the xenobiotics by often enhancing their reactivity and/or the water
solubility through the addition of oxygen atom. A two-component flavin diffusible
monooxygenase family (TC-FDM) (Galan et al. 2000) is a monooxygenase that
plays a role in the degradation of environmental pesticide residues. The cytochrome
P450 family is another large group of monooxygenase enzymes that have a wide
substrate range and have been reported to catalyze biochemically recalcitrant
reactions, such as oxidation or hydroxylation of non-activated carbon atoms
(Werck-Reichhart et al. 2000). An example of the use of cytochrome P450 in the
bioremediation of herbicides is cytochrome CYP1A1 (also known as aryl hydrocarbon hydroxylase) from mammalian liver, which has been found to degrade atrazine,
norflurazon and chlortoluron (Kawahigashi et al. 2005).
50
A. Sehrawat et al.