Enzyme Lab #3: The Effect of pH on an Enzyme
An individual enzyme works well only over a small pH range. Although some, like stomach enzymes, work at low pH (pH 1-2) and others work at or near neutrality, enzymes do not tolerate a large pH swing. In this lab, you will investigate pH change on catalase, an enzyme which catalyses the decomposition of hydrogen peroxide into hydrogen gas and oxygen gas.
- 1 red potato
- 3% hydrogen peroxide
- white vinegar
- small test tubes
- plastic cups
- 20 ml. graduated cylinder
- masking tape
- test tube rack
- transfer pipettes
- *optional- pH meter or pH paper
After preparing and filtering a red potato into a plastic cup, as previously described, set up five test tubes in a test tube rack; label them A-E. To each test tube, add 2 ml. hydrogen peroxide and the following:
- 4 drops vinegar
- 1 drop distilled water
- 2 drops vinegar, 2 drops distilled water
- 1 drop vinegar, 3 drops distilled water
- 4 drops distilled water
(At this point the students can take the pH of each test tube with some pH paper or a pH meter or the teacher can explain that the pH of test tube A is less than that of B, B is less than C, C is less than D, and D is less than E because of dilution.)
Now add 2 dropperfuls of catalase to each test tube. After a minute or two, measure the height of the foam produced in each test tube. Record these amounts.
- With what vinegar-water mixture or at which pH did the catalase work best? (produce the most foam)
- Where was it least effective?
- Construct a line graph of test tube or pH vs. foam height.
- What does your graph say about the influence of pH on catalase activity? Be as specific as possible.
Are enzymes equally effective at all pH levels? Explain your answer.
The potato, 3% hydrogen peroxide, 5% white vinegar, cheesecloth, and plastic cups are available at the grocery store and some pH strips in the swimming pool section of a local hardware store.