Immobilised enzymes

• what are the 4 methods for immobilising enzymes

  adsorption, covalent bonding, entrapment and membrane separation
• advantages of immobilising enzymes

  1. enzymes do not mix with product so extraction cost is lower
  2. enzymes can be reused
  3. continuous process is made easier as there are no cells requiring nutrients, reproducing and releasing waste products
  4. enzymes surrounded by immobilising matrix which protects them from extreme conditions so high pH and temperatures can be used
• describe adsorption

  enzymes are bound to a supporting surface by hydrophobic interactions and ionic links. Surfaces can be clay, porous carbon, glass, beads and resins. Enzymes are bound so active site is exposed, but can be slightly distorted. Bonds aren't always strong so enzymes can become detached and leak into reaction mixture.
• describe covalent bonding

  enzymes bound to supporting surface (e.g. clay) using strong covalent bonds. Bonded using a cross-linkage agent, which may also link them in a chain. Production can be expensive and can distort active site. Less likely to become detached.
• describe entrapment

  enzymes are trapped in a matrix that does not allow free movement. Enzymes are unaffected by this and remain fully active. Substrate molecules must diffuse into entrapment matrix and product must diffuse out. Therefore only suitable for small molecules Calcium alginate beads are often used. Industrial processes may use cellulose mesh.
• describe membrane separation

  enzymes separated from reaction mixture by a partially permeable membrane. substrate and product must be small enough to pass through the membrane by diffusion. this may limit reaction rate
• give examples of uses of immobilised enzymes

  • glucose isomerase- produces high fructose corn syrup which is sweeter than sucrose
  • penicillin acylase- formation of semi-synthetic penicillin as some microbes aren't resistant to these types
  • lactase-hydrolysis of lactose to glucose and galactose so milk can be used as a calcium source for lactose intolerant people
  • aminoacylase- production of L-amino acids which are used in pharmaceuticals
  • glucoamylase- converts dextrins into glucose