Investigation: Enzymes


Title: The effect of pH on Catalase Catalyzed Reactions

Purpose: To test the effects of pH on the rate of enzymatic reaction catalyzed by catalase.

Background: Enzymes are proteins produced by our cells, that act as biological catalysts. Catalysts increase the rate of a reaction by lowering the activation energy needed for the reaction to begin. This is important, because although catalyzed reactions will occur eventually, oftentimes in order to create the products needed by life, the reactions need to occur more quickly. Enzymes act as catalysts in our cells, binding with substrates and lowering the activation energy required for the reaction to occur. Substrates (the reactants in the chemical reaction) bind to the active site of the enzyme. Enzymes are substrate specific, and the substrate whose reaction the enzyme catalyses fits in to the active site almost perfectly, like a lock and key. Factors that effect the rate of enzymatic reactions include: pH, Temperature, presence of inhibitors and activators, concentration of the enzyme and concentration of the substrate. Catalase is an enzyme that functions in cells, converting H2O2 into oxygen and water. Catalase is found in animals, plants and humans, particularly in the liver of humans and animals. Catalase functions at an optimum pH of 7.0 (neutral). The surroundings in which catalase operates naturally most often have a neutral pH and a temperature of 37 Degrees Celsius. 

Hypothesis: If pH has an impact on the rate of catalase reactions, then the reactions with a more acidic pH will occur more slowly or not at all.

Materials: Catalase extracted from Cow liver, H2O2, , Distilled Water, Lemon Juice, pH reader, beakers, dropper, graduated tubes, long, plastic tubes.

Equipment Setup:


  1. Fill graduated tube with 10 ml of H2O2
  2. Fill beaker with 200 ml of water. Place the upside down graduated tube with a hole in the lid into the beaker of water, press it down so that it fills with water. This tube is used for measurements.
  3. Attach the end of the tube to the bottom of the upside down graduated tube with a hole in the lid into the water.
  4. Attach the other end of the tube to the lid of the other graduated tube containing H2O2
  5. Place binder clips near each end of the tube.
  6. Add acid/add base/add nothing (for neutral)
  7. Add 2 drops of the enzyme to the H2O2
  8. Quickly screw on lid of graduated tube with the H2O2 and
  9. Remove binder clips and start the timer, hold graduated tube in water steady and in a way that can be read. Do not move this tube.
  10. Record the amount of oxygen in mL produced after 10, 20, 30, 40, 60, 80, 100, 200, 300 and 400 seconds, by looking at how far the water in the graduated tube at that end has moved.

Data Table

Screen Shot 2013-10-27 at 7.15.16 PM

*Temperature does not have any further bearing on this experiment. Data was collected merely for interest. 




           This graph shows that the rate of the reaction at a pH of 4.7, rising from 0 to 5.5 in 140 seconds (aprox. .34mL/10seconds), was quicker than the reaction with a pH of 3.4, which took 400 seconds to produce 1 ml of oxygen (.0025mL/10seconds).  The rate of the reaction with the pH of 2.5 was the slowest (0mL of O2 per 10 seconds),  the reaction did not produce any (measurable) oxygen. 


 The results supported the hypothesis, the rate of reaction with the normal pH of catalase, 4.7, was greater than the reactions with the added acidity. This is shown by the data: The reaction at the pH of 4.7 produced approximately .34mL of oxygen in every ten seconds. The approximate slope of the line of best fit is for a pH of 4.7 is significantly larger than the slope of the line of best fit for a pH of  3.4 is, and the pH of 2.5 had a slope of zero.


            The hypothesis was supported because catalase is built to function under certain conditions in certain environments. One of these environmental factors is pH, and because H2Ohas a normal pH of 4.7, catalase operates best at this temperature because it is meant to react with H2O2. When catalase is placed in a solution with an extreme change, the enzyme may become “denatured” and lose its structure. The protein structure of the enzyme will change, which changes the function of the enzyme. Because enzymes are substrate specific, when the shape of the enzyme changes, the substrate no longer fits into the active site. Because enzymes aren’t used up in one reaction and are expected to be used over and over again, this impacts not only one set of reactions, but the whole series of reactions.

         Enzymes impact how rapidly the reaction occurs. When enzymes are affected, the reaction rate will slow down. This allows scientists to test what factors effect the enzymes and how the enzymes are effected based on how quickly the reaction occurred. 

             In order to ensure that experimental error was kept to the minimum, as many variables were kept as constant as possible. These variables included: amount of water in the beakers and graduated cylinders, the temperature, the concentration of H2O2, the concentration of the enzyme (catalase), the presence of inhibitors (not present), and the equipment setup.   Some error in measurement could be do to moving the tube where we were reading the oxygen, other errors could have arisen because of differences of temperature in the environment or slight differences in procedure because different groups were conducting these tests. Errors could have also arisen if there were any undetected leaks remaining in the equipment after it was checked.  Possible errors in measurement occurred in the reaction at the pH of 3.4, the first values likely remained at zero because the reaction occurred slowly, and it took the oxygen produced that long to move across the tube between the beakers.  

Works Cited:

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