Investigating the influence of pH on catalase

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Fair test:

        As we are dealing with the influence of pH on catalase, in order to give a fair test, we should focus only on the pH and keep the following the same:

1. Enzyme concentration --- by using the same potato
2. Substrate concentration --- by keeping the amount and volume of hydrogen peroxide the same
3. Temperature --- by doing it in the same laboratory in the same day
4. Size and surface area of the enzyme --- by making sure that all single piece of small potato cut is the same size
5. Time --- by allowing the reaction to last only two minutes each time

Prediction:

        I predict that the rate of reaction would be greatest in a range of pH with an optimum because I think a particular enzyme works best in a particular range of pH. For the catalase, I think the rate of reaction would be fastest with pH7.

Result:

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Analysis:

        From the graph drawn which shows the rate of oxygen gas produced at different pH, we can see that the reaction starts off with a low value i.e. 2.25 cm3 / min at pH3. And then as the pH increases, the rate of reaction increases vigorously. But it decreases slightly at pH 8 after it reaches it maximum of 10.25 cm3 / min at pH7.

Conclusion:

        From the basic AS Biology knowledge, for every enzyme there is an optimum pH at which the reaction it catalyses most rapidly. Many enzymes work within a pH range of 5 – 9 and catalyse reactions most efficiently at pH7. There are exceptions. For example, stomach work best at pH1.5 – 2.5. Alkaline phosphatase in the kidneys has an optimum pH of 10.

        The symbol pH refers to the concentration of hydrogen ions in a solution. The concentration of hydrogen ions [H+] affects the stability of the electrovalent bonds, which help to maintain the tertiary structure of protein molecules. A small change in pH means relatively large changes in [H+]. E.g. a change of 1 on the pH scale involves a ten-fold increase or decrease in [H+] while a change in pH of 2 represents a hundred–fold change in [H+]. Thus even small changes in pH can have a great effect on enzyme activity.

        There are few effects on the enzyme due to the change in pH. Proteins are denatured by changes in pH because the change in pH affects the ionisation of amino acids. As the ionisation of constituent amino acids changes, their ionic bonds, which help to stabilise protein shape are broken. As a result, the protein changes shape. This will then lead to the change of the shape of the active site of the enzyme, which means that the enzyme no longer fits the substrate, so it is said to be denatured. Besides, the ionisation of substrate molecules can also be affected. The formation of enzyme–substrate complexes sometimes depends on the active centres, and substrate molecules having opposite electrostatic changes. If the changes are altered by changes in pH, some enzyme fail to function.

        From the result obtained, graph drawn, analysis and the basic knowledge of Biology, I came to a conclusion that the enzyme catalase from the experiment I had done functions quite efficiently over the range of pH3 - 8 and works best at pH7 which I think is the optimum pH for catalase and this is what I predicted. And I believe that the reaction rate will slightly decrease or even won’t work if pH like pH1, pH2, pH11, pH12, pH13, and pH14 is used. Because these pHs which is probably out of the range of pH for catalase will destroy the tertiary structure of protein and the enzyme will be denatured.

Evaluation:

        This was not an excellent experiment as there were some limitations and possible errors occurred.

Limitations:

As there were only pH3, 4, 5, 6, 7, 8 six different pH available, I couldn’t fully prove that those other pHs wouldn’t give a fast reaction rate as pH7, or which of them are out of the range of pH for catalase that are meant to make the enzyme denatured.

Possible errors:

There were several possible errors which could have made the results I obtained inaccurate like

1. temperature --- as I was not doing the whole experiment in the same day, there might have been a slight temperature difference in those two different days which affect the reaction.
2. potato --- as I was using different packs of potato which means that reaction rate might have been affected because some potato might not react so well with hydrogen peroxide as the other did.

        Luckily, there weren’t any anomalous results.

        

        But if I had a chance to do this experiment again I would reduce all the possible errors and limitations I faced this time as many as possible. In order to do this, I will have to keep those variables, which I mentioned before like:

1. Enzyme concentration --- by using potato from the same pack to make sure consistency
2. Substrate concentration --- by using exactly 10 ml of 20 volume of hydrogen peroxide each time
3. Temperature --- because when I finished the experiment in two different day, although I was doing it in the same laboratory, there might still have a slight difference in temperature which could have affected the result I obtained. So to make sure this kind of things will not happen again, I will have to do the whole experiment in a row within the shortest time in the same day without rushing to get the most accurate result
4. Size and surface area of the enzyme --- by making sure that 20 small pieces of potato are cut each time with 5mm × 5mm
5. Time for the reaction --- by keeping the time for reaction the same
6. Besides I may use a different buffers e.g. a buffer with pH6 – 14 to see if it will show a different result.

The end!