Objective: To observe the effect of pH on catalase enzyme in potato protein extract       

Background: Hydrogen peroxide is a byproduct of several metabolic reactions in living cells. If allowed to accumulate it can cause oxidative damage. Therefore, it is constantly removed by catalase which decomposes it to water and oxygen. Catalase is found in nearly all living organisms exposed to oxygen. The optimum pH of catalase in potatoes is about 7. In this lab, you will observe the effect of changing pH conditions on catalase enzyme activity by reacting hydrogen peroxide with catalase present in potato protein extract (pH 3.5 – 7.5).      

SAFETY PRECAUTION: You will be working with 30% hydrogen peroxide. This concentration is capable of oxidizing your skin, usually causing a bleaching effect. Please use gloves.


  • 30% hydrogen peroxide
  • Potato protein extract
  • LabQuest oxygen detector apparatus
  • Clamp
  • Stir bar
  • Stir plate
  • Pipette
  • Pipette tips    


  1. Collect 50 ml of potato protein extract in two separate 150 ml beakers
  2. Using 0.1 M NaOH and 0.5 M HCl, adjust extract to the following pH
    • Lab Group # 1: 7 and 3.5
    • Lab Group # 2: 7 and 4.5
    • Lab Group # 3: 7 and 5.5
    • Lab Group # 4: 7 and 6.5
    • Lab Group # 5: 7 and 7.5
  3. Transfer sample with pH = 7 to the oxygen detection sample bottle and add stir bar 
  4. Add 1 ml of 30% hydrogen peroxide to the sample bottle and begin oxygen detection using LabQuest. Collect data (oxygen in ppm) for 10 minutes
  5. Transfer your data to the whiteboard for the class to record
  6. Repeat the procedure with the second adjusted sample
  7. Create a graph showing oxygen concentration in ppm (y-axis) versus time in minutes (x-axis) for each pH level. Note: Since everyone will collect readings at pH 7, the pH 7 oxygen readings should be averaged. Plot all 6 curves on the same graph (i.e. pH = 3.5, 4.5, 5.5, 6.5, 7.0 and 7.5)

Lab Questions

  1. Based on the graph, was 7.0 the optimum pH for catalase in potato? If not, which pH was optimum based on your findings? Is this supported by literature?
  2. Where does hydrogen peroxide come from in living systems? What is the role of catalase in living systems?
  3. How does pH affect the structure, shape, and biological activity of enzymes?

Courtney Simons
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.
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