89
of serine proteases is well studied. The serine residue is a characteristic in the active
site of this enzyme group. Serine proteases are the most widely distributed group of
proteolytic enzymes. They are tolerant to high alkaline pH though the optimum is at
7–11. The diverse serine proteases are classified into 20 families. Barett (1994)
reports that there are six clans and that they are supposed to have common ancestors. The sequence analysis of the four clans, chymotrypsin (SA), subtilisin (SB),
carboxypeptidase C (SC) and Escherichia D-Ala–D-Ala peptidase A (SE), shows
wide differences among them, leading to the conclusion that they are descended
from various origins.
The compound diisopropyl fluorophosphate (DFP) can inhibit the enzyme activity. Tosyl-L-lysine chloromethyl ketone and phenyl methyl sulphonyl fluoride are
also found to inhibit serine proteases. Serine proteases hydrolyse an amide bond at
the carboxyl end of the polypeptide which has tyrosine, phenylalanine or leucine
residues.
3.4.3.5 Aspartic Proteases
Aspartic proteases can exhibit biorestriction of insect pests. They are mostly active
at a pH of 3–4. Many reports on them show a fungal origin, though bacterial and
protozoan candidates are present. In the active site they possess two aspartate residues which are conserved.
3.4.3.6 Cysteine/Thiol Proteases
A promising group of enzymes in biocontrol is Cysteine/thiol proteases which have
occurrence in plants, animals and prokaryotes. The activity of all cysteine proteases
depends on a catalytic dyad consisting of cysteine and histidine (Barrett and
McDonald 1986). From different sources, they exhibit different pH optima. They
can function at acidic or alkaline pH. For activity, they need the proximity of
Hydrogen Cyanide (HCN) or cysteine-like reducing agents. A classical example of
cysteine protease is papain and it has best activity around pH 7. But lysosomal proteases exhibit maximum activity at acidic pH. Cysteine proteases are affected by
sulfhydryl agents, but it is reported that EDTA or DFP does not impair activity.
3.4.3.7 Metalloproteases
Metalloproteases possess metal ions, often Zn
2+,
Co
2+,
Mn
2+
, and are affected by
EDTA because it can chelate metal ions, and are insensitive to sulphydryl agents.
The reactivation is enabled by providing the required metal ions. They are maximally active at a pH of 5–9. They were isolated and characterised from bacteria and
fungi. The stability of domain structure is maintained by calcium. The list of various
protease-producing biocontrol agents and the pathogens affected by tyhem are
given in Table 3.4.
3 Enzymes for Bioremediation and Biocontrol
of serine proteases is well studied. The serine residue is a characteristic in the active
site of this enzyme group. Serine proteases are the most widely distributed group of
proteolytic enzymes. They are tolerant to high alkaline pH though the optimum is at
7–11. The diverse serine proteases are classified into 20 families. Barett (1994)
reports that there are six clans and that they are supposed to have common ancestors. The sequence analysis of the four clans, chymotrypsin (SA), subtilisin (SB),
carboxypeptidase C (SC) and Escherichia D-Ala–D-Ala peptidase A (SE), shows
wide differences among them, leading to the conclusion that they are descended
from various origins.
The compound diisopropyl fluorophosphate (DFP) can inhibit the enzyme activity. Tosyl-L-lysine chloromethyl ketone and phenyl methyl sulphonyl fluoride are
also found to inhibit serine proteases. Serine proteases hydrolyse an amide bond at
the carboxyl end of the polypeptide which has tyrosine, phenylalanine or leucine
residues.
3.4.3.5 Aspartic Proteases
Aspartic proteases can exhibit biorestriction of insect pests. They are mostly active
at a pH of 3–4. Many reports on them show a fungal origin, though bacterial and
protozoan candidates are present. In the active site they possess two aspartate residues which are conserved.
3.4.3.6 Cysteine/Thiol Proteases
A promising group of enzymes in biocontrol is Cysteine/thiol proteases which have
occurrence in plants, animals and prokaryotes. The activity of all cysteine proteases
depends on a catalytic dyad consisting of cysteine and histidine (Barrett and
McDonald 1986). From different sources, they exhibit different pH optima. They
can function at acidic or alkaline pH. For activity, they need the proximity of
Hydrogen Cyanide (HCN) or cysteine-like reducing agents. A classical example of
cysteine protease is papain and it has best activity around pH 7. But lysosomal proteases exhibit maximum activity at acidic pH. Cysteine proteases are affected by
sulfhydryl agents, but it is reported that EDTA or DFP does not impair activity.
3.4.3.7 Metalloproteases
Metalloproteases possess metal ions, often Zn
2+,
Co
2+,
Mn
2+
, and are affected by
EDTA because it can chelate metal ions, and are insensitive to sulphydryl agents.
The reactivation is enabled by providing the required metal ions. They are maximally active at a pH of 5–9. They were isolated and characterised from bacteria and
fungi. The stability of domain structure is maintained by calcium. The list of various
protease-producing biocontrol agents and the pathogens affected by tyhem are
given in Table 3.4.
3 Enzymes for Bioremediation and Biocontrol