3.2.4—Immobilised enzymes
- Syllabus
- 9700–2028–2029
- Objective
- 3.2.4
- Level
- AS
Immobilised enzymes trade access speed for control and reuse
A free enzyme is added to the reaction solution. An immobilised enzyme is bound to an inert, stationary, insoluble support such as alginate, while substrate is brought to the support and product is collected separately.
| Feature | Free enzyme | Immobilised enzyme |
|---|---|---|
| Reaction system | Enzyme is mixed into the solution with the substrate | Enzyme is retained on an insoluble support; substrate must reach the support |
| Access and observed rate | Direct mixing can make substrate access rapid | Access through/around the support can limit the observed rate |
| Product separation | Enzyme remains mixed with the product | Product can be collected without carrying the enzyme into the product |
| Recovery and reuse | Recovery from the reaction mixture is difficult | Support can be retained and the enzyme reused for repeated processing |
| Stability and process control | Conditions act directly on enzyme in solution | Immobilisation can increase tolerance of pH and temperature changes and supports controlled processing |
- Compare equal reaction times and measure product formed per unit time, not just the final product amount.
- Keep substrate concentration, pH, temperature, total volume and measurement method the same.
- Match the starting catalytic amount as closely as possible and keep support amount/size consistent when comparing immobilised preparations.
- Repeat both treatments and compare representative means; a lower observed rate may reflect access or support effects rather than an intrinsically different enzyme mechanism.
In a supported lactase process, milk is passed over alginate beads containing lactase. Lactose is hydrolysed to glucose and galactose while the enzyme remains associated with the support, allowing the product stream to be collected and the preparation reused.
Immobilisation does not make an enzyme permanently stable, guarantee a faster rate, or justify claims that enzyme can never leave the support. Judge the measured system using matched controls and the same time basis; do not invent column dimensions or other apparatus specifications.
Follow the limiting step across the topic
A rate change is evidence about the current bottleneck, not an explanation by itself. Ask whether the observation is best explained by collision frequency, substrate availability, usable active-site capacity, enzyme shape or diffusion.
- A substrate plateau shows that enzyme capacity now limits rate; the plateau approaches Vmax.
- Half of Vmax locates Km on the substrate-concentration axis.
- If more substrate restores the original maximum, competition for active sites is supported.
- If the maximum remains lower, functional enzyme capacity has been reduced.
- If immobilised enzyme appears slower, diffusion may be limiting even though reuse and separation improve.
To make a valid conclusion, change one factor, control the others, compare initial rates and stay within the tested range. A single point cannot establish a curve shape or inhibitor type.
ConceptA-Level CAIE Biology AS