6.4.8 immobilised enzymes

Question 1

disadvantages of immobilised enzymes

Answer 1

• product must be isolated from enzymes before use = expensive
• setting up process is expensive
• immobilised enzymes often less active than free enzymes = process is slower

Question 2

advantages of immobilised enzymes

Answer 2

• don’t mix with product, so extraction costs are lower
• enzymes easily reused
• continuous process is made easier, as no cells requiring nutrients, reproducing & releasing waste products
• enzymes surrounded by immobilising matrix, protecting them from extreme conditions = wider pH range & higher temperature used without denaturing

Question 3

4 methods of immobilising enzymes

Answer 3

1. adsorption
2. covalent bonding
3. entrapment
4. membrane separation

Question 4

describe adsorption

Answer 4

• enzyme molecules bound to supporting surface with active site exposed = accessible to substrate
• combination of hydrophobic interactions & ionic links
• surfaces include: clay, porous carbon, glass beads & resin

negatives:
- active site may be distorted by additional interactions = affects enzyme activity
- bonding forces not always strong, so enzyme can become detached/leak into reaction mixture

Question 5

describe covalent bonding

Answer 5

• enzyme molecules bonded to supporting surface by strong covalent bonds (eg. clay)
• enzymes bonded using cross-linking agent, possibly linking them in chain

negatives:
- production of covalent boding can be expensive & distort active site = reduces activity
positives:
- enzymes less likely to leak/become detached

Question 6

describe entrapment

Answer 6

• enzyme molecules trapped in matrix which doesn’t allow free movement
• schools often use calcium alginate beads to immobilise enzymes
• industrial processes may use cellulose mesh

positives:
- enzyme molecules unaffected & remain fully active
negatives:
- substrate molecules must diffuse into entrapment matrix & product molecules must be able to diffuse out = method only suitable for processes where substrate/products are relatively small

Question 7

describe membrane separation

Answer 7

• enzyme molecules separated from reaction mixture by partially permeable membrane

negatives:
- product/substrate molecules must be small enough to pass through membrane by diffusion
- access to enzymes may limit reaction rate