Immobilised Enzymes

Question 1

What are immobilised enzymes?

Answer 1

They are enzymes that are fixed in place so that they do not mix freely with the substrate and are not lost in the process

Question 2

Explain how enzymes can be immobilised through adsorption

Answer 2

• enzymes are mixed with the immobilising support (e.g. clay or glass beads) and bind to it due to a combination of hydrophobic interactions and ionic links
• because the bonding forces are not particularly strong, enzymes can become detached (leakage)
• however, provided the enzyme molecules are held so that their active site is not changed and is a displayed adsorption rates can give very high reaction rates

Question 3

Explain how enzymes can be immobilised through covalent bonding

Answer 3

• enzyme molecules are covalently bonded to a support, often by covalently linking enzymes together and to an insoluble material (e.g. clay particles) using a cross linking agent
• 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

Question 4

Explain how enzymes can be immobilised through entrapment

Answer 4

• enzymes may be trapped in a gel bead or network or cellulose fibres
• the enzymes are trapped in their natural state
• however, reaction rates can be reduced because substrate molecules need to get through the trapping barrier
• this means the active site is less easily available than with adsorbed or covalently bonded enzymes

Question 5

Explain how enzymes can be immobilised through membrane separation

Answer 5

• enzymes may be physically separated from the substrate mixture by a partially permeable membrane
• 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

Question 6

Explain why immobilised enzymes are used in large scale production

Answer 6

• enzymes do not mix with products - so purification costs are low
• enzymes are immediately available for reuse
• enzymes are more stable - immobilising matrix protects the enzymes