Chapter 3: Enzymes
BOX 3.2: Immobilised enzymes Figure 3.15 shows one way in which enzymes can be immobilised. The enzyme is mixed with a solution of sodium alginate. Little droplets of this mixture are then added to a solution of calcium chloride. The sodium alginate and calcium chloride instantly react to form jelly, which turns each droplet into a little bead. The jelly bead contains the enzyme. The enzyme is held in the bead, or immobilised. These beads can be packed gently into a column. A liquid containing the enzyme’s substrate can be allowed to trickle steadily over them (Figure 3.16). As the substrate runs over the surface of the beads, the enzymes in the beads catalyse a reaction that converts the substrate into product. The product continues to trickle down the column, emerging from the bottom, where it can be collected and purified.
milk
alginate beads containing immobilised lactase
milk free of lactose and lactase mixture of sodium alginate solution and lactase 65
Figure 3.16 Using immobilised enzyme to modify milk. When small drops of the mixture enter calcium chloride solution, they form ‘beads’. The alginate holds the enzyme molecules in the beads.
Figure 3.15 Immobilising enzyme in alginate.
QUESTIONS 3.10 a Outline an investigation you could carry out to
compare the temperature at which the enzyme lactase is completely denatured within 10 minutes i when free in solution, ii when immobilised in alginate beads. b Outline an experiment you could carry out to investigate how long it takes the enzyme lactase to denature at 90 °C i when free in solution, ii when immobilised in alginate beads.
c Outline how you would determine the optimum pH of the enzyme lactase i when free in solution, ii when immobilised in alginate beads. 3.11 Summarise the advantages of using immobilised enzymes rather than enzyme solutions.