Immobilization of Enzymes
Shudhangshu Shekhar Kundu
What an enzyme?
Enzymes are protein molecules, which serve to accelerate the chemical reactions of living cells (often by several orders of magnitude). Without enzymes, most biochemical reactions would be too slow to even carry out life processes. Enzymes display great specificity and are not permanently modified by their participation in reactions. Since they are not changed during the reactions, it is cost-effective to use them more than once. However, if the enzymes are in solution with the reactants and/or products it is difficult to separate them.
What is Immobilization?
Immobilization is being in a stationary phase or unable to move.
What is Immobilization of Enzymes?
It is a method in which an enzyme is attached to an inert, insoluble material that will prevent loss of enzyme activity by not changing the chemical nature or reactive groups in the binding site of the enzyme. Eg., Sodium alginate.
Methods of Immobilization:
The surface on which the enzyme is immobilized is responsible for retaining the structure in the enzyme through hydrogen bonding or the formation of electron transition complexes.
These links will prevent vibration of the enzyme and thus increase thermal stability. The micro environment of surface and enzyme has a charged nature that can cause a shift in the optimum pH of the enzyme of up to 2 pH units.
This may be accompanied by a general broadening of the pH region in which the enzyme can work effectively, allowing enzymes that normally do not have similar pH regions to work together.
• Carrier-Binding: the binding of enzymes to water-insoluble carriers. • Cross-Linking: intermolecular cross-linking of enzymes by bi-functional or multi-functional reagents. • Entrapping: incorporating enzymes into the lattices of a semi-permeable gel or enclosing the enzymes in a semi-permeable polymer membrane.
Carrier binding Method:
In 1916s Nelson and Griffin discovered that artificial carrier-bound invertase on Aluminium hydroxide and charcoal was catalytically active, the potential of bio-immobilization as a method of obtaining useful and reusable immobilized biocatalysts. In these early days, bio-immobilization was mainly carried out by adsorption on simple inorganic carriers such as glass alumina or hydrophobic compound-coated glass.
In 1950s the method of enzyme immobilization was dominated by non-specific physical adsorption of enzymes or proteins on solid carriers (physical method), examples: • α-amylase adsorbed on activated carbon,
• chymotrypsin on kaolinite
• DNase on cellulose etc.,
Along with physical methods of enzyme immobilization, other methods like covalent immobilization were further investigated. Examples: lipases and other enzymes or antibodies covalently bound to polyaminostyrene.
Apart from these, for the first time, was shown by Dickey that some enzymes such as AMP deaminase entrapped in the sol–gel inorganic matrix formed by silicic acid derived glasses, retained reasonable biological activity. Unfortunately, the importance of this finding was not recognized in the succeeding 40 years.
In this method, the amount of enzyme bound to the carrier and the activity after immobilization depend on the nature of the carrier. The selection of the carrier depends on the nature of the enzyme itself, as well as the: • Particle size
• Surface area
• Molar ratio of hydrophilic to hydrophobic groups
• Chemical composition
In general, an increase in the ratio of hydrophilic groups and in the concentration of bound enzymes, results in a higher activity of the immobilized enzymes. Some of the most commonly used carriers for enzyme...
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