Use of immobilized enzymes in bioprocesses offers many advantages, including greater productivity because the same enzyme molecules can be used over a long period of time, there is more precise control of the extent of reaction, there is the capability of automation and continuous operation, and the elimination of the requirement of a downstream enzyme inactivation step (1 ). The ease and cost of immobilized enzyme preparation has limited commercial application of enzyme bioreactor processes. In this chapter a method for immobilization of enzymes using the high affinity, bioselective interaction between biotin and avidin is described. Avidin, which is a tetrameric protein, binds four biotin molecules with a dissociation constant of about 10−15 (2 ) thus, it represents one of the strongest noncovalent interactions known. Vis-a-vis adsorption by ion-exchange interaction, the avidin-biotin interaction is very specific and much stronger; therefore, enzyme leaking from the support is minimal, resulting in greater operational stability (3 –9 ). Furthermore, the biotin molecule is very robust; consequently, bioreactors can be repeatedly regenerated simply by desorption of inactive enzyme in a chaotropic solvent, followed by selective adsorption of avidin and finally, fresh biotinylated enzyme.
