Enzymes are catalysts
Enzymes act as catalysts in metabolicreactions. Features of enzymes that make them so useful in industrial processes are;
- Specificity-enzymes can catalyse reactions between specific chemicals, even in mixtures of many different chemicals. This means that fewer by-products are formed and less purification of products is necessary
- temperature of enzyme action-most enzymes function well at relatively low temperatures, much lower than those needed for many industrial chemical processes.This saves a great deal of money on fuel costs. However, enzymes from thermophilic bacteria-bacteria that thrive at high temperatures, have been extracted and used in reactions that need a high temperature.
In the biotechnological processes previously described, whole organisms are cultured on a large scale to generate particular products. in many areas of clinical research and diagnosis and in some industrical processes, the product of a single chemial reaction rather than frowing the whole organism or using an inorganic catalyst.
Isolated enzymes can be produced in large quantities in comerial biotechnological processes. The extraction from the fermentation mixture is known as downstreaming processing-the process involved in separation and purification of any product of large-scale fermentations.
in order for the product of an enzyme-controlled reaction to be generated, enzyme and substrate must be able to collide and form enzyme-substrate complexes. This is most easily achieved by mixing quantities of substrate and isolated enzyme together under suitable conditions for the enzyme to work. The product generated then needs to be extracted from the mixture. This can be a costly process.
It is possible to imobilise enzymes so that they can continue to catalyse the enzyme controlled reaction but do not mix freely with the substrate as they would normally in a cell or isolated system.
- Enzymes are not present with products so purifications/downstream processing costs are low
- Enzymes are immediately available for reuse. This is particularly useful in allowing for continuous processes
- Immobilised enzymes are more stable because the immobilising matrix protects the enzyme molecules
DISADVANTAGES of immobilising enzymes
- Immobilisation requires additional time, equipment and materials and so is more expensive to set up
- Immmobilised enzymes can be less active because they do not mix freely with substrates
- any contamination is costly to deal with because the whole system would need to be stopped.
methods for immobilising enzymes
Four possible methos for immobilising enzymes. The precise method used for a particular process depends on a range of factors including ease of preparation, cost, relative importance of enzyme 'leakage' and efficiency of the particular enzyme that is immobilised.
Adsorption and covalent bonding involve binding enzymes to a support, whereas entrapment and membrane separation hold them in place without binding.
- enzyme molecules are mixed with the immobilised support and bind to it due to a combination of hydrophobic interactions an iconic links.
- Adosorbing agents including porus carbon, glass beads, clays and resins.
- Because the bonding forces are not particularly strong, enzymes can become detatched-leakage.
- However, provided the enzyme molecules are held so that their active site is not changed and is displayed, adsorption can give very higreaction rates.
- Enzyme molecules are covenlently bonded to a support, often by covalent linking enzymes together and to an insoluble material-clay-using a cross-linking agent like gluteraldehyde or sepharose.
- this method does not immobilise a large quantity of enzyme but binding is very strong so there is very little leakage of enzyme from the support.
- Enzymes may be trapped, e.g. in a gel bead or a network of cellulose fibres.
- The enzymes are trapped in their natural state e.g. not bound to another molecule so their ative site will not be affected.
- However, reaction rates can be reduced because substrate molecules need to get through the rapping barrier.
- This means the active site is less easily available than with adsorbed or covalently bonded anzymes
Methods and Usage
- Enzymes may be physically separated from the substrate mixture by a partially permeadble membrane.
- Most simply, the enzyme solution is held at one side of a membrane whilst substrate solution is passed along the other side.
- Substrate molecules are small enough to pass through the membrane so that the reaction can take place. Product molecules are small enough to pass back through the membrane
PRODUCING NEW ANTIBIOTICS
- There has been an increase in the number of antibiotic-resistant strains of pathogenic bacteria in recent years
- Scientific research into developing new antibiotics often focuses on chainging the structure of available antibiotics so that the target microorganisms are no longer resistant.
- Immobilised penicillin acyclase enzyme reactors have been used to convert the antibiotic penicillin into amino penicillanic acid on a large scale
- The amino penicillanic acid is then used as a base molecule to procude a range of different penicillin-type antibiotics.