A5 - Enzyme Immobilization

(A. Rosevear, J. F. Kennedy and J. M. S. Cabral²²)

Enzyme immobilization is a process where the movement of the enzyme is severely restricted in space in such a way that its catalytic activity is still preserved. Enzyme immobilization allows continuous use and reuse of the catalyst.

Some advantages of the immobilized enzymes over their soluble forms are:

• increased enzyme stability
• reduced enzyme costs
• greater ease of enzyme separation and recovery for reutilization
• possibility of operating continuously
• easy product separation
• reduced effluent problems
• and , in some cases, increased activity.

Despite this advantages industrial application is still limited by:

• the comparatively low cost of soluble enzymes
• traditional attitudes
• the investment needed for introducing new equipment to already implanted processes
• the nature and cost of the immobilizing support and the immobilizing process (including losses of activity)
• the performance of the system

The choice of the matrix is very important for the good performance of an immobilized enzyme system. It is then desirable that an enzyme carrier possesses:

• large surface area
• permeability
• hydrophilic character
• insolubility
• chemical, mechanical and thermal stability
• high rigidity
• suitable shape and particle size
• resistance to microbial attack
• regenerability

Alternatively it is also possible to immobilize, either viable or non-viable, whole cells. This is of great help when cofactors and/or several enzymes are needed at the same time. However, side reactions are possible and thus less pure products are obtained.

Classification of Immobilized Enzymes

The term immobilized enzyme includes:

• enzymes modified to a water insoluble form
• soluble enzymes retained within reactors by a non-permeable ultrafiltration membrane
• soluble enzymes with their mobility restricted by attachment to another molecule.

The classification of the immobilization methods for enzymes presented here is based on the nature of the interaction and the nature of the support used.