© Pearson Education Ltd 2009 This document may have been altered from the original Describe how enzymes can be immobilised Adsorption onto clay, resin, glass beads and porous carbon. Enzymes are held on the surface by hydrophobic interactions and ionic links. Good exposure of active sites. Enzyme not tightly bound so may leach off surface and be lost. Bonding may affect active site. Covalent bonding to other enzyme molecules and to a support. Enzyme tightly bound so little leakage from support but cannot bind large amounts of enzyme. Bonding may affect active site. Entrapment within a gel bead or cellulose fibres. Reaction rates can be slowed because substrate molecules have to get through the gel or fibres to get to the active site. Membrane separation Partially permeable membrane separates enzyme and substrate. Substrate passes through, reaction takes place, products pass back through membrane to be collected. Immobilised Enzymes

© Pearson Education Ltd 2009 This document may have been altered from the original a)Adsorption on clay etc b) Covalent linking c) Trapped in fibres

© Pearson Education Ltd 2009 This document may have been altered from the original Explain why immobilised enzymes are used in large- scale production. ADVANTAGES Enzymes are kept separate from the products so purification costs are low Enzymes immediately available for re-use, no need for complicated extraction process Immobilised enzymes are more stable because the immobilising matrix protects the molecules (eg from temperature changes or pH changes) Immobilised Enzymes

© Pearson Education Ltd 2009 This document may have been altered from the original Explain the problems with immobilised enzymes in large- scale production. DISADVANTAGES Immobilising enzymes is more expensive Immobilised enzymes may give slower reaction rates as molecules do not mix freely with substrate molecules Substrate has to diffuse into bead structures or through mesh Contamination is more difficult to deal with Immobilised Enzymes

Immobilised organisms Sometimes microorganisms are immobilised instead of individual enzymes. Advantages Enzymes unlikely to leach out into product Microorganisms make the enzymes necessary Disadvantages Reaction rates may be slower as substrate has to enter through cell membrane Other unwanted products may be made in addition to the required one, these then need separating out.