An immobilised enzyme is an enzyme that is attached to, or held inside, an insoluble material so that it cannot mix freely with the substrate solution. The substrate solution flows over or through the enzyme, and the product flows out without the enzyme.Methods of immobilisation
• Adsorption: enzyme molecules are bound to the surface of an insoluble support such as clay, porous carbon or glass beads, by hydrophobic interactions and ionic bonds. Enzymes may leak off.
• Covalent bonding: enzymes are covalently bonded to a support such as cellulose or collagen fibres. They are held very firmly, but the bonding can alter the active site.
• Entrapment: enzymes are trapped in a matrix such as alginate beads or silica gel. The substrate must diffuse into the matrix to reach the enzyme.
• Membrane separation: enzymes are kept on one side of a partially permeable membrane, which the small substrate and product molecules can pass through.
Advantages
• The enzyme does not contaminate the product, so less downstream processing is needed.
• The enzyme can be recovered and reused many times, reducing cost.
• Immobilised enzymes are often more stable, so they work over a wider range of temperature and pH.
• Suits continuous processes.Disadvantages
• Extra equipment and materials make the setup more expensive.
• The rate of reaction may be lower, because substrate cannot reach the active sites as easily.
• If enzymes leak or become contaminated, they are harder to replace.
• Adsorption: enzyme molecules are bound to the surface of an insoluble support such as clay, porous carbon or glass beads, by hydrophobic interactions and ionic bonds. Enzymes may leak off.
• Covalent bonding: enzymes are covalently bonded to a support such as cellulose or collagen fibres. They are held very firmly, but the bonding can alter the active site.
• Entrapment: enzymes are trapped in a matrix such as alginate beads or silica gel. The substrate must diffuse into the matrix to reach the enzyme.
• Membrane separation: enzymes are kept on one side of a partially permeable membrane, which the small substrate and product molecules can pass through.
Advantages• The enzyme does not contaminate the product, so less downstream processing is needed.
• The enzyme can be recovered and reused many times, reducing cost.
• Immobilised enzymes are often more stable, so they work over a wider range of temperature and pH.
• Suits continuous processes.Disadvantages
• Extra equipment and materials make the setup more expensive.
• The rate of reaction may be lower, because substrate cannot reach the active sites as easily.
• If enzymes leak or become contaminated, they are harder to replace.