CHEMICAL METHODS OF IMMOBILIZATION

Covalent bonding and ionic bonding are used to bind the enzyme to the support and thus immobilize the enzyme.

Covalent Bonding
The enzyme is made to covalently bind to the support. Surface modification (of the support) is usually the first step in enzyme immobilization by covalent bonding.

Cellulose, Carboxy methyl cellulose, Dextrose, Agarose are some of the important supports in covalent attachment. The choice of the support depends on the surface properties.
The support should have functional groups that facilitate the attachment/covalent bonding of the enzyme to the support.
If the support doesn't have the functional groups essential for attachment of enzymes, they should be modified/activated.
In many covalent immobilization processes the first step is surface modification or activation. Two common methods of surface modification or surface activation are :

• Silanisation
• Attachment of flexible spacer arm moeties.

Silanisation
An organofunctional silane group is coated onto the support. such coatings are then derivatized to aldehyde groups using glutaraldehyde to which enzymes are attached.

Attachment of flexible spacer arm moeties
Flexible spacer arm moeties such as n-propyl amine are attached to the support. They offer more flexibility and the enzyme attached to them have their structure better protected.

Advantages

• Enzyme activity is high.
• Substrate specifity of the enzyme is changeable.
• The strong covalent attachments hold the enzyme tightly and thus contribute to the stability by preventing the deactivation of the enzyme.

Disadvantages

• Covalent interaction between substrate and enzyme disturb the native enzyme structure.
• Regeneration of enzyme is impossible.
• Preperation is difficult.
• Cost is high.

Ionic Bonding
The enzyme is made to bind to the support through ionic bonding.

DEAE sephadex, DEAE cellulose, DOllen-50, Carboxymethyl Cellulose and amberlite are the supports usually used.

Advantages

• Low cost.
• Regeneration is possible.
• Preperation is easy.
• Overall enzyme activity is high.

Disadvantages

• Not fit for industrial use.
• Ionic interactions between substrate and enzyme disturbs the enzyme activity.
• Effectiveness gradually decreases.
• Substrate specificity is unchangeable.