Enzyme Activity and pH

Test Tube pH Height of foam (cm)
1 3.0 4.5
2 5.5 5.5
3 7.0 10.0
4 10.0 4.0
5 13.0 0


Students in biology class tested the pH specificity of the enzyme catalase. Catalase is present in all living cells. This enzyme breaks down hydrogen peroxide, toxic to cells, into water and oxygen gas.

Procedure:
1. 2 mL of hydrogen peroxide was added to five clean test tubes.
2. The pH of each test tube was manipulated using 1M HCl (an acid) and/or 1M NaOH (a base). By adding HCl or NaOH drop by drop the pH was manipulated to reach the following:
Test tube 1 – pH 3
Test tube 2 – pH 5
Test tube 3 – pH 7
Test tube 4 – pH 10
Test tube 5 – pH 13


3. 1 mL of liver puree was added to each test tube. Observations were made. If there was evidence of gas production (foam), the level of foam was measured in centimeters and recorded. Student data can be seen in the table above.

What does this experiment indicate about enzyme specificity?

The optimum pH for catalase activity is 7.
The enzyme catalase was denatured at pH 13.
According to the experiment, the optimum temperature for catalase activity is 22C.
Hydrochloric acid makes the stomach pH low, between 1.5 to 3.5: catalase activity would not occur in the stomach.
Catalase lowers the activation energy needed to decompose hydrogen peroxide.