3.2 Factors that Affect Enzyme Action

Neutrase® is an enzyme that is used to hydrolyse proteins in solution. When the enzyme is mixed with a 2% protein solution the reaction mixture changes from white to colourless.

A student carried out an experiment to find the effect of copper sulfate and potassium sulfate on the activity of Neutrase®.

The student made four reaction mixtures in test tubes A to D. Test tubes A to C contained equal volumes of protein solution and 0.1 cm³ of solutions of copper sulfate or potassium sulfate. Test tube D contained the same volume of protein solution and 0.1 cm³ of water.

0.5 cm³ of a 1% Neutrase® solution was added to test tube A and immediately placed into a colorimeter. The colorimeter was used to measure the intensity of light that is absorbed by the solution (absorbance) over 100 seconds. The procedure was repeated with the other reaction mixtures, B, C and D.

The results are shown in Fig. 1.

Fig. 1

With reference to Fig. 1:

• Describe the effects of copper sulfate solution and potassium sulfate solution on the activity of Neutrase®
• Suggest explanations for the effects that you have described.

Neutrase® can be immobilised in alginate. Immobilised Neutrase® is used in the food industry to produce foods with high nutritional content.

Explain the advantages of using immobilised enzymes, such as Neutrase®, compared with using the same enzymes free in solution.

The unicellular fungus Kluyveromyces lactis is found in dairy products. It is a safe microorganism to culture for the extraction of the enzyme lactase.

Lactase catalyses the breakdown of lactose, a sugar found in milk.

The reaction catalysed by lactase is summarised in Fig. 1.

Fig. 1

Describe the reaction that is catalysed by lactase. Use Fig. 1 to help you.

In your answer, identify Y and product Z.

On a commercial scale, immobilised lactase can be used to produce lactose-free milk.

One of the products of the reaction shown in Fig. 1 acts as an inhibitor of lactase. This is an example of product inhibition.

(i)

Explain why product inhibition is useful in K. lactis when lactase is acting as an intracellular enzyme, but can be a disadvantage when extracted lactase is used free in solution for the production of lactose-free milk.

[2]

(ii)

Suggest how using immobilised lactase for the production of lactose-free milk helps to reduce the problem of product inhibition.

[1]

(iii)

The first large-scale production of lactose-free milk with an immobilised enzyme used lactase trapped in cellulose triacetate fibres.

Suggest one feature of cellulose triacetate that makes it useful as an immobilising material.

When developing an enzyme-catalysed reaction for use in industry, the progress of the reaction is studied.

Outline how the progress of an enzyme-catalysed reaction can be investigated experimentally.

Explain the effect that increasing the concentration of an enzyme would have on the rate of a reaction.

Sketch a graph showing enzyme concentration against the rate of reaction when the amount of substrate is limited.

Hydrogen peroxide is broken down by the enzyme catalase into water and oxygen. Catalase can be found inside most types of living cells, including potato cells.

A group of students investigated the effect of various concentrations of hydrogen peroxide on the reaction rate of catalase. They ground up a 3 cm piece of potato cylinder with 5 cm³ of distilled water to provide a solution containing catalase. They then made a serial dilution of the original 100 % stock solution of hydrogen peroxide before setting up three test tubes for each concentration of hydrogen peroxide. For each test tube, they dipped a filter paper disc into the catalase suspension and placed the disc at the bottom of the test tube containing 10 cm³ of hydrogen peroxide. They measured the time taken for the disc to float up to the surface of the hydrogen peroxide solution.

Their results are shown in Table 1.

Table 1

Calculate the reaction rate for the 100% hydrogen peroxide concentration. Show your working.

Explain the results of the investigation shown in Table 1.

Trypsin is an enzyme produced by the pancreas that hydrolyses proteins in the small intestine. 

The activity of trypsin was investigated by placing a small amount of the enzyme with a known concentration of protein.

Fig. 1 shows the progress of this reaction when it is carried out at 25 °C.

Fig. 1

Calculate the initial rate of the reaction in Fig. 1. Show your working.

The procedure was repeated at the same temperature in the presence of a competitive inhibitor of trypsin.

Predict the results that will be obtained using the competitive inhibitor.

Describe how your prediction for part (b) would be different if a non-competitive inhibitor was used rather than a competitive inhibitor.

The investigation was extended to compare the initial reaction rates of trypsin obtained from different species of animals. 

Suggest two advantages of calculating the initial reaction rates of enzyme catalysed reactions here rather than the reaction rates at another point during the experiment.

Researchers immobilised an amylase enzyme in alginate beads. They investigated the effects of temperature on the activity of the immobilised amylase compared with amylase that was free in solution.

The results for this investigation are shown in Fig. 1.

Fig. 1

Compare the effects of temperature on the activity of immobilised and free amylase shown in Fig. 1.

When the researchers immobilised amylase they had to ensure that the size of the alginate beads were all the same.

Suggest and explain one reason why using different sized alginate beads would affect the activity of immobilised amylase.

State one variable other than bead size that the researchers should keep constant in this investigation.

[1]

Explain your answer to part (i).

[1]

State three advantages of using immobilised enzymes in industrial processes.

Fig. 1 shows the disaccharide lactose, which is found in milk.

Fig. 1

Name the type of bond that joins the two monosaccharides in lactose.

The enzyme lactase catalyses the breakage of the bond between the two monosaccharides in lactose.

(i)

Name the type of reaction that breaks this bond.

[1]

(ii)

Some people do not produce the enzyme lactase, so cannot digest lactose.

The presence of lactose in the lumen of the intestine reduces the volume of water absorbed into the blood, resulting in diarrhoea.

Suggest why the presence of lactose in the intestine reduces the volume of water absorbed.

[2]

Enzymes, such as lactase, are often immobilised for use in the food industry.

A scientist carried out an investigation to determine the effects of temperature on the activity of lactase when it was immobilised and when it was free in solution.

The scientist produced alginate beads containing lactase for use in this investigation. The beads varied in size. The scientist selected small beads for the investigation and put them into a glass column.

(i)

Suggest the advantage of using small beads rather than large beads.

[2]

(ii)

Fig. 2 shows the results of the investigation to determine the effects of temperature on the activity of lactase when it was immobilised, I, and when it was free in solution, F.

Fig. 2

With reference to Fig. 2, compare the effect of temperature on the activity of immobilised lactase, I, and lactase free in solution, F.