Immobilized enzyme

An immobilised enzyme is an enzyme which is attached to an inert, insoluble material such as sodium alginate.

In 1916 Nelson and Griffin discovered that invertase “exhibited the same activity when absorbed on a solid (charcoal or aluminium hydroxide) at the bottom of the reaction vessel as when uniformly distributed throughout the solution”. This discovery was the first of various enzyme immobilization techniques currently available.

Besides absorption, different covalent methods of enzyme immobilization were developed in the 1950s and 1960s. Up to now, more than 5000 publications and patents have been published on enzyme immobilization techniques. Several hundred enzymes have been immobilized in different forms and approximately a dozen immobilized enzymes, for example penicillin G acylase, lipases, proteases, invertase, etc. have been used as catalysts in various large scale processes.

Commercial use
Immobilised 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.
 * Economical: 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.

Immobilisation of an Enzyme
There are four different ways in which one can immobilise an enzyme which are the following:
 * Adsorption on glass or alginate beads: Enzyme is attached to the outside of an inert material
 * Covalent Binding: Cross-linkage to another chemical e.g. cellulose or glyceraldehydes.
 * Entrapment in a silica gel: Enzyme is held in a mesh or capsule of an inert material.
 * Membrane confinement: Enzyme is put on one side of a semi-permeable membrane, allowing reactant and resultant product to pass in and then out of the membrane.