The effect of pH on the activity of catalase

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The effect of pH on the activity of catalase

Introduction

        An enzyme called catalase catalyses the breakdown of hydrogen peroxide, into oxygen and water. Catalase is a heme containing redox enzyme. It is found in high concentrations in a compartment in cells called the peroxisome. The formula for the breakdown of hydrogen peroxide is:

                2H2O2     2H2O   +   O2

H2O2 is a powerful oxidising agent and is potentially damaging to cells, and it is formed during aerobic respiration. By preventing excessive H2O2 build up, Catalase allows important cellular processes that produce H2O2 as a by-product to take place safely.

        A suitable source of catalase is provided by minced potato and in the experiment the pH is varied using citric acid-sodium phosphate buffer solutions at pH values of 4.4, 5.2, 6.5 and 7.5.

Materials

  • Citric acid-sodium phosphate solutions. These solutions are made up as follows: Solution A is 21 g citric acid H20 dm-3. Solution B is 28.4 g anhydrous disodium hydrogen phosphate (Na2HPO4) dm-3. Buffer solutions are prepared by mixing solutions of A and B in the volumes shown in the table below.
  • Hydrogen peroxide solution, 10 volume
  • Minced Potato
  • 5cm3 or 10 cm3 plastic syringe with the end cut off to measure the minced potato
  • Graduated pipette or syringe to measure buffer solutions
  • Stopwatch
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Composition of citric acid-sodium phosphate buffer solutions at various pHs

Method

  1. Set up apparatus as shown in diagram below.
  2. Place 3 cm3 of minced potato in the conical flask and add 10 cm3 of buffer solution. Swirl gently to mix.
  3. Replace the bung in the flask ensuring an airtight seal. Fill the graduated tube with water and invert it carefully into the beaker of water. Do not place over the end of the delivery tube.
  4. Measure 5 cm3 of hydrogen peroxide into the syringe and connect to the flask. Inject the hydrogen peroxide. ...

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