How Does pH Affect the Efficiency of Catalase?
CLAIM
An enzyme is a biological catalyst that works to speed up chemical reactions in
living systems without being consumed by the reaction. Different factors that can
affect an enzyme’s efficiency include temperature, pH and the concentration of the
enzyme (Reece et al., 2011).
Each enzyme has an optimum pH at which it works at and it depends on where in
the body the enzyme works (Pickering, 2010). For example, pepsin, which is found
in the stomach and aids in the digestion of proteins, works best at a pH of 1-2 (Reece
et al., 2011). Catalase is an enzyme that aids in the decomposition of hydrogen
peroxide into water and oxygen. It is found in high concentrations in perioxisomes
and has an optimum pH of 7 (Crook, 2003). Catalase is found in many fruits and
vegetables, such as potatoes, bananas, onions and cherries, as well as in the liver in
the human body (Nuffield Foundation, 2011; Reece et al., 2011).
EVIDENCE
Data Table 1: Time Taken for Catalase-Soaked Discs to Rise in Hydrogen Peroxide
Solution
pH
1
4
7
9
14
Time Taken for Disc to Rise (s)
Trial Number
1
2
3
15.0
17.2
16.8
9.4
10.2
9.8
1.0
1.4
1.3
6.2
7.4
7.3
17.8
18.1
17.4
Average
Time (s)
16.3
9.8
1.23
6.97
17.77
Rate (1/s)
0.06
0.10
0.81
0.14
0.06
Figure 1: How pH Effects the Rate of Enzyme Catalysis
0.9
0.8
Rate (1/s)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
REASONING
2
4
6
8
10
12
14
16
pH
As can be seen in Figure 1, the optimum pH for catalase is 7. This is where the
fastest rate of reaction is observed. The enzyme catalase is most efficient in a neutral
pH, so it is expected that it would be most efficient at pH 7 (Crook, 2003).
From Figure 1, the enzyme is not efficient in highly acidic and highly basic
environments (pH 1 and pH14) and only marginally more efficient in slightly acidic
and slightly basic environments (pH 4 and pH 9). Extremely high or low pH values
result in a complete loss of activity for most enzymes (Bennett & Frieden, 1969).
Each enzyme works within a small pH range, and changes in the pH can make and
break intramolecular and intermolecular bonds, which change the shape of the
enzyme and its effectiveness (Enzymes, 2012). This is evident from the extremely
low reaction rates of the catalase outside of its optimal pH range.
REBUTTAL
Questions that arises from this laboratory are why do different enzymes have
different optimum pH values and why don’t enzymes function at all pH values?
Different enzymes don’t have the same optimal pH value because they are found in
different parts of our body. Pancreatic lipase, which breaks down lipids, has an
optimum pH of 8. This suggests that the pancreas is a slightly basic environment.
Pepsin, which breaks down proteins in the stomach, has an optimum pH of 2. This
suggests that the stomach is a highly acidic environment. Catalase, which breaks
down hydrogen peroxide in the liver, has an optimum pH of 7. This suggests that the
liver is a neutral environment (Reece et al., 2011).
An enzyme does not function efficiently in all pH values because they become
denatured (change the 3-D shape) in pH values outside of their optimum range. If an
enzyme becomes denatured, the substrate molecules can not bind to the enzyme
and therefore, no products will be produced (Pickering, 2010; Reece et al., 2011).
REFERENCES
Bennett, T. P., and Frieden, E. (1969). Modern Topics in Biochemistry. London, UK:
Macmillan.
Crook, J. (2003). Catalase – An Extraordinary Enzyme. Accessed September 18,
2012. http://www.catalase.com/cataext.htm.
Enzymes (no publication date). Chemistry for Biologists. Accessed September 18,
2012. http://www.rsc.org/Education/Teachers/Resources/cfb/enzymes.htm.
Nuffield Foundation (2011). Microscale Investigations of Catalase Activity in Plant
Extracts. Accessed September 18, 2012.
http://www.nuffieldfoundation.org/practical-biology/microscale-investigationscatalase-activity-plant-extracts.
Pickering, R. (2010). Complete Biology for Cambridge IGCSE. Oxford, UK: Oxford
University Press.
Reece, J. et al. (2011). Campbell Biology, 9th Edition. San Francisco, USA: Pearson
Education Inc.