Immobilized enzyme

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

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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 three different ways in which one can immobilise an enzyme which are the following, and are listed in order of effectiveness:

• Adsorption on glass, alginate beads or matrix: Enzyme is attached to the outside of an inert material. Generally speaking, 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.
• Entrappment: 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.

See also

• Immobilized whole cell