Immobilised enzymes

• what is an immobilised enzyme?

  enzyme molecules bound to an inert material, over which the substance molecules move
• how are enzymes immobilised?

  • when they are fixed, bound or trapped on an inert matrix (e.g. sodium alginate beads or cellulose microfibrils)
  • these can be packed into glass columns
  • substrate is added to the top of the column and as it flows down, its molecules bind to the enzymes molecules’ active sites, both on the bead surface and inside the beads as the substrate molecules diffuse in
  • once set up, the column can be used repeatedly
  • enzyme is fixed and doesn’t contaminate the products - so they are easy to purify
• how many times can an immobilised enzyme be used?

  multiple times
• why are the products easy to purify?

  as the immobilised enzyme is fixed and doesn’t contaminate the products
• where are immobilised enzymes used?

  they are widely used in industrial processes, such as fermentation, as they can readily be recovered for reuse
• why are enzymes, rather than inorganic catalysts, used widely in industry?

  • they are more efficient
  • have a higher turn-over number
  • they are very specific
  • more economical as they work at lower temperatures
• if small beads are made, how will it affect the rate of reaction?

  if small beads are made, the substrate molecules will have easier access to enzyme molecules and so they will produce a higher rate of reaction
• what is a factor preventing the wider use of enzymes that are free in solution?

  enzyme instability
• what can denature enzymes, with a consequent loss of activity?

  • organic solvents
  • high temperatures
  • extremes of pH
• why is immobilising enzymes with a polymer matrix making them more stable?

  as it creates a microenvironment allowing reactions to occur at higher temperatures or more extreme pHs than normal
• what does trapping an enzyme molecule do?

  it prevents the shape change that would denature its active site, so the enzyme can be used in a wider range of physical conditions than if it were in a free solution
• what does this graph show?

  its showing the effect of temperature on the rate of reaction of the same enzyme in its free and in its immobilised state

  
• why do enzymes immobilised in beads have a lower rate of reaction than those immobilised on a membrane (if all other factors are constant)?

  • this is because some of the active sites are inside the beads and the substrate takes time to diffuse to them
  • enzymes on a membrane are readily available for binding, so they gave a higher reaction rate
• what are some advantages on immobilised enzymes?

  • increased stability and function over a wider range of temperatures and pH than enzymes free in solution
  • products aren’t contaminated with the enzyme
  • enzymes are easily recovered for use
  • a sequence of columns can be used so several enzymes with differing pH or temperature optima can be used in 1 process
  • enzymes can be easily added or removed, giving greater control over the reaction