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Investigation into the effect of different ph levels and hydrogen peroxide concentrations on the activity of potato tissue catalase.

The investigation was carried out to determine how different ph levels and hydrogen concentrations, affect the activity of catalase in potato during the decomposition of hydrogen peroxide to produce water and oxygen. Different variables (independent, dependent and controlled) were put into consideration during the laboratory session to find out how much oxygen was produced. The test was carried out, using potato as a source of catalase and reacting it with hydrogen peroxide and ph. Five different ranges were used for the two variables and each test was repeated 3 times with new pieces of potato discs and the volume of oxygen was measured. The result of the investigation showed that, the enzyme catalase worked at its optimum at 30% which was the highest range available and an optimum ph of 9. The result above illustrates that catalase in potato works best at high ph levels and substrate concentrations.

INTRODUCTION

The purpose of this experiment was to determine the optimal substrate concentrations and ph levels under which enzymatic reactions involving the enzyme catalase will occur successfully. Catalase is a heme containing enzyme usually found in high concentrations in cellular organelles called peroxisomes (www1).

Catalase disproportionate:

2H2O2 → 2H2O + O2

Catabolic reactions provide raw materials and energy to start up various anabolic activities (www2). According to Brooker, Widmaier, Graham and Stiling (2008), catalase is a type of enzyme found mainly in the liver cells where they break down toxic hydrogen peroxide into less reactivegaseous oxygen and water molecules which is useful to the human body. Catalysts are not used up in reactions but affect the rate of the reaction by reducing the amount of activation energy required (Brooker et al., 2008).

Enzymes are globular proteins and have a three dimensional shape (www3). They are biological catalysts which speeds up the rate of chemical reactions without been used up (www3). Allen and Baker (1982) states that, extreme variations in the concentration of hydrogen ions and substrate concentrations could change the structure of the active site and disrupt the substrate from binding to the active site and this will prevent the formation of the enzyme substrate complex. Enzymes will be denatured, if the optimum ph and substrate concentrations at which they work best are altered and this will result in inactivity of the reaction (www3). Catalase works best at high levels of substrate concentration and ph levels, therefore the higher the concentrations of each variable, the more oxygen will be produced when molecules of hydrogen peroxide are free (Brooker et al., 2008).

METHODS

*See laboratory schedule*.

The two independent variables in the investigation were ph and hydrogen peroxide. Each individual enzyme catalase has its own ph and substrate characteristics, this is as a result of the hydrogen and ionic bonds that make the unique primary structure of an enzyme.

The 5 ranges of substrate concentrations used for the experiment differed from each other in terms of concentration. The ph levels differed from each other but during the experiment, 1ml of the different levels of ph was added to 1ml of 10 % hydrogen peroxide.

The dependent variable in the catalase investigation was the volume of oxygen measured.

The controlled variable in this investigation were the temperature of the room, size and number of potato discs used for the experiment because this was the variable that made the results of the investigation valid.

RESULTS

Below are the results for the reaction of hydrogen peroxide in the presence of potato catalase.

Table 1: The effect of different substrate concentrations on catalase activity.

H2O2 concentration

Volume of oxygen measured (ml)

Mean

Test 1

Test 2

Test 3

0%

0

0

0

0

5%

4

3

3

3.3

10%

9

9.6

8.6

9

20%

9.1

9

9.2

9.1

30%

10

10

10

10

Fig 1: Attached

The optimum condition for the substrate concentration was 30 %. The line of best fit is a straight line through the origin then the reaction rate had a slight curve before the optimum substrate level was reached.

Below are the results for the reaction of ph in the presence of potato catalase.

TABLE 2: The effect of different ph levels on catalase activity in potato.

PH

Volume of Oxygen Measured (ml)

Mean

Test 1

Test 2

Test 3

3

6.8

5.8

7

6.5

5

8.2

6.8

6.4

7.1

7

8.2

6.6

8.4

7.7

9

10

10

10

10

11

7.2

6.8

7.8

7.2

Fig 2: See attached

The optimum ph level for the enzyme catalase was 9. The line of best fit shows that, after this point the rate of the reaction decreased.

DISCUSSION

The result of the catalase investigation proves the information retrieved from the source Brooker et al., 2008 is right. The reaction increases with increasing enzyme concentration when molecules of hydrogen peroxide are freely available until the optimum level is reached (Brooker et al., 2008). The increase in the rate of reaction is limited when molecules of the substrate are in short supply and this because there are different number of variables that aids in determining the decomposition of hydrogen peroxide in the presence of the enzyme catalase. According to www1, increase in enzyme concentration means there are more active sites for the substrate molecules to bind with and greater quantity of products can be attained. At 30%, there were many active sites but insufficient number of substrate molecules to occupy the active site. From the line of best fit shown on the graph, they might be some anomalies and this would have happened as a result of slight inaccuracies, fluctuating room temperatures which may have caused the gas to expand in the boiling tube.

The result for ph as shown on the graph shows a clear pattern of the enzyme at its optimum point and when it gradually loosed its activity and became denatured, this supports the information that was referred to in the introduction (Allen and Baker, 1982 and www2). As the ph increased the volume of oxygen produced increased until the enzyme catalase reached its optimum at ph 9. After the optimum ph level as seen on the graph, the volume of oxygen produced gradually decreased which means there were insufficient substrate molecule to occupy the active site and the enzyme catalase lost its ability to function effectively. Denaturing of enzymes is irreversible because the bonds between the 3 dimensional shapes of the enzyme has been altered.

Conclusion

The investigation has shown that the activity of catalase in potatoes can be affected by changes in different ph levels and hydrogen peroxide concentrations. The reaction reached its optimum at 30% substrate concentration and ph 9 respectively. Looking at the graph of both variables, it clearly shows that further increase in the ranges used in the experiment would have resulted in decrease in the volume of oxygen gas produced and there would have been free active sites with no substrate to occupy it and this will limit the reaction and radically continue to reduce the rate of reaction.

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