11.6 Immobilization of Enzymes
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reagents such as glutaraldehyde. In any form of chemical immobilization, it is important that the active site of the enzymes is not altered; otherwise, the enzyme is
destroyed. Therefore, the functional groups involved are those which do not affect
the enzyme’s activity.
Natural polymers are also used in chemical immobilization of enzymes. Agarose
is commonly used for such application. Polymers generally have minimal reactivity
with enzymes; therefore, when used for immobilization of enzyme, polymers are
first activated with reagents prior to contacting with the enzymes. This pretreatment
is targeted at freeing up specific functional groups on the polymer to allow covalent
reaction with the inactive sites on the enzyme.
11.6.2 Physical Immobilization
In the physical method, immobilization can be achieved by entrapment, microencapsulation or adsorption of the enzyme within or unto a support. The adsorption
method makes use of surface-active compounds unto which the enzymes are physically adsorbed. Cellulose and collagen are examples of natural polymers used as
adsorbents for physical enzyme immobilization. Other adsorbents are calcium carbonate, alumina, clays and glass plates. Hydroxyapatite, although not a polymer,
is also an interesting material used as physical enzyme immobilization adsorbent
which occurs naturally in the aquatic environment. Hydroxyapatite is present in the
scales of fish where it makes up part of the extracellular matrix. Adsorption method is
particularly preferred as a method of enzyme immobilization as it is relatively simple
process, it is reversible and there is little chance of the enzyme being deactivated in
the process of immobilization. It, however, has the disadvantage of the weak bond
between the enzyme and the support which are mainly due to secondary molecular
interactions unlike the chemical method which are formed with covalent bonds.
The entrapment method makes use of cross-linked polymers within which the
enzymes are trapped. The polymer is mixed with the enzyme prior to cross-linking.
The enzyme dispersed within the polymer is then trapped within the network upon
cross-linking. In the microencapsulated method, the enzymes are placed in the
semipermeable membrane microcapsules. The microcapsules are formed using interfacial polymerization where the enzymes are encapsulated within the droplets of
polymers formed. This method yields an immobilized enzyme system with high
surface area.
11.7 Environmental Implications
Table 11.3 gives a summary of consumption in the process of a typical enzyme
extraction process using the method presented by Bele et al. (2014a, b) as an example
case study. The reader should note that the processes vary for different feedstocks.
249
reagents such as glutaraldehyde. In any form of chemical immobilization, it is important that the active site of the enzymes is not altered; otherwise, the enzyme is
destroyed. Therefore, the functional groups involved are those which do not affect
the enzyme’s activity.
Natural polymers are also used in chemical immobilization of enzymes. Agarose
is commonly used for such application. Polymers generally have minimal reactivity
with enzymes; therefore, when used for immobilization of enzyme, polymers are
first activated with reagents prior to contacting with the enzymes. This pretreatment
is targeted at freeing up specific functional groups on the polymer to allow covalent
reaction with the inactive sites on the enzyme.
11.6.2 Physical Immobilization
In the physical method, immobilization can be achieved by entrapment, microencapsulation or adsorption of the enzyme within or unto a support. The adsorption
method makes use of surface-active compounds unto which the enzymes are physically adsorbed. Cellulose and collagen are examples of natural polymers used as
adsorbents for physical enzyme immobilization. Other adsorbents are calcium carbonate, alumina, clays and glass plates. Hydroxyapatite, although not a polymer,
is also an interesting material used as physical enzyme immobilization adsorbent
which occurs naturally in the aquatic environment. Hydroxyapatite is present in the
scales of fish where it makes up part of the extracellular matrix. Adsorption method is
particularly preferred as a method of enzyme immobilization as it is relatively simple
process, it is reversible and there is little chance of the enzyme being deactivated in
the process of immobilization. It, however, has the disadvantage of the weak bond
between the enzyme and the support which are mainly due to secondary molecular
interactions unlike the chemical method which are formed with covalent bonds.
The entrapment method makes use of cross-linked polymers within which the
enzymes are trapped. The polymer is mixed with the enzyme prior to cross-linking.
The enzyme dispersed within the polymer is then trapped within the network upon
cross-linking. In the microencapsulated method, the enzymes are placed in the
semipermeable membrane microcapsules. The microcapsules are formed using interfacial polymerization where the enzymes are encapsulated within the droplets of
polymers formed. This method yields an immobilized enzyme system with high
surface area.
11.7 Environmental Implications
Table 11.3 gives a summary of consumption in the process of a typical enzyme
extraction process using the method presented by Bele et al. (2014a, b) as an example
case study. The reader should note that the processes vary for different feedstocks.