2.4.2 Immobilised Enzymes

Immobilised enzymes are widely used in industry

• Just before 1900, it was discovered that enzymes could be used to catalyse production of alcohol in the absence of yeast cell
• Since then, hundreds of enzymes have been developed outside of living cells for commercial purposes
• Uses of enzymes in industrial processes can be expensive, so we need ways to reuse them in order to be cost-effective
• An immobilised enzyme is an enzyme that is attached to an insoluble material to prevent mixing with the product and through this method, the enzyme can be reused in subsequent reactions
• Immobilised enzymes are used in the following commercial processes
  • Agriculture
  • Biosensors (diagnosis, analysis eg. for impurities)
  • Manufacturing processes
  • Energy generation
  • Environmental management
  • Food/drinks industry
  • Medicines

• Methods by which enzymes can be immobilised include:
  • Attachment to an inert substance eg. glass
  • Entrapment within a matrix e.g. alginate gel
  • Entrapment within a partially permeable membrane

Different ways in which enzymes can be immobilised

• The mechanism of immobilised enzyme use works as follows:
• • The immobilised enzymes are contained within a column
  • The substrate is filtered through this column in solution
  • As the substrate runs through the column, enzyme-substrate complexes are formed and products are produced
  • These products then flow out of the column, leaving the enzymes behind to catalyse the reaction again

The immobilised enzymes are contained within a column

Advantages of immobilised enzymes

• There is no enzyme in the product (the product is uncontaminated) and therefore there is no need to further process or filter the end product
• The immobilised enzyme can be reused multiple times which is both efficient and cost-effective (many enzymes are expensive)
  • Reusing the enzyme also avoids the need to separate the enzyme from the product in downstream processing

• Immobilised enzymes have a greater tolerance of temperature and pH changes (immobilisation often makes enzymes more stable)
• Substrates can be exposed to higher enzyme concentrations than when using enzymes in solution, increasing the rate of throughput
• Conditions can be controlled carefully, allowing immobilised enzymes to function close to their optimum conditions and be more stable

Disadvantages of immobilised enzymes

• Specialist expensive equipment is required
• Immobilised enzymes are more costly to buy, so are unlikely to be financially worthwhile for smaller industries
• The rate of reaction is sometimes lower when using immobilised enzymes as the enzymes cannot mix freely with the substrate

Examples of immobilised enzymes in industry

A closer look at lactose-free milk production

• • Milk is a valuable source of nutrients containing protein, fat and the carbohydrate lactose
  • 5-10% of the UK population are lactose intolerant
    • They can't digest lactose and suffer from bloating, digestive problems, discomfort and pain

  • Lactose is a disaccharide that is hydrolysed into glucose and galactose
  • The yeast Kluyveromyces lactis grows naturally in milk and can be cultured as a source of the enzyme lactase
  • Glucose and galactose are sweeter than lactose, so less sugar needs to be added to foods with modified lactose to achieve the same sweetness
  • Ice cream and yoghurt production also benefit from having more glucose and galactose than lactose in the milk they are made from

Using the immobilised enzyme lactase to modify milk