An immobilized enzyme is an enzyme that is attached to an inert, insoluble material such as calcium alginate (produced by reacting a mixture of sodium alginate solution and enzyme solution with calcium chloride). This can provide increased resistance to changes in conditions such as pH or temperature. It also allows enzymes to be held in place throughout the reaction, following which they are easily separated from the products and may be used again - a far more efficient process and so is widely used in industry for enzyme catalysed reactions. An alternative to enzyme immobilization is whole cell immobilization.
Immobilized enzymes are very important for commercial uses as they possess many benefits to the expenses and processes of the reaction of which include:
- Convenience: Minuscule amounts of protein dissolve in the reaction, so workup can be much easier. Upon completion, reaction mixtures typically contain only solvent and reaction products.
- Economy: The immobilized enzyme is easily removed from the reaction making it easy to recycle the biocatalyst.
- Stability: Immobilized enzymes typically have greater thermal and operational stability than the soluble form of the enzyme.
In the past, biological washing powders and detergents would contain many proteases and lipases which would break down dirt. However, when the cleaning products would come into contact with the skin, it would create allergic reactions. This is why immobilization of enzymes are important, not just economically.
Immobilization of an Enzyme
There are three different ways by which one can immobilize an enzyme, which are the following, listed in order of effectiveness:
- Adsorption on glass, alginate beads or matrix: Enzyme is attached to the outside of an inert material. In general, this method is the slowest among those listed here. As adsorption is not a chemical reaction, the active site of the immobilized enzyme may be blocked by the matrix or bead, greatly reducing the activity of the enzyme.
- Entrapment: The enzyme is trapped in insoluble beads or microspheres, such as calcium alginate beads. However, this insoluble substances hinders the arrival of the substrate, and the exit of products.
- Cross-linkage: The enzyme is covalently bonded to a matrix through a chemical reaction. This method is by far the most effective method among those listed here. As the chemical reaction ensures that the binding site does not cover the enzyme's active site, the activity of the enzyme is only affected by immobility. However, the inflexibility of the covalent bonds precludes the self-healing properties exhibited by chemoadsorbed self-assembled monolayers. Use of a spacer molecule like poly(ethylene glycol) helps reduce the steric hindrance by the substrate in this case. Enzymes may also be immobilized to a surface using non-covalent or covalent Protein tags.
-  Article on enzyme immobilization.