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Enzyme Action: Testing Catalase Activity


Many organisms can decompose hydrogen peroxide (H2O2) enzymatically. Enzymes are globular proteins, responsible for most of the chemical activities of living organisms. They act as catalysts, as substances that speed up chemical reactions without being destroyed or altered during the process. Enzymes are extremely efficient and may be used over and over again. One enzyme may catalyze thousands of reactions every second. Both the temperature and the pH at which enzymes function are extremely important. Most organisms have a preferred temperature range they survive in, and their enzymes most likely function best within that temperature range. If the environment of the enzyme is too acidic or too basic, the enzyme may irreversibly denature, or unravel until it no longer has the shape necessary for proper functioning.

H2O2 is toxic to most living organisms. Many organisms are capable of enzymatically destroying the H2O2 before it can do much damage. H2O2 can be converted to oxygen and water, as follows:

2 H2O2 --> 2 H2O + O2

Although this reaction occurs spontaneously, enzymes increase the rate considerably. At least two different enzymes are known to catalyze this reaction: catalase, found in animals and protists, and peroxidase, found in plants. A great deal can be learned about enzymes by studying the rates of enzyme catalyzed reactions.

In this experiment, you will measure the rate of enzyme activity under various conditions, such as different concentrations of enzyme, pH values, and temperatures. It is possible to measure the pressure of oxygen gas formed as H2O2 is destroyed. If a plot is made, it may appear similar to that of Figure 1.

Figure 1

At the start of the reaction, there is no product, and the pressure is the same as the atmospheric pressure. After a short time, oxygen accumulates at a rather constant rate. The slope of the curve at this initial time is constant and is called the initial rate. As the peroxide is destroyed, less of it is available to react and the O2 is produced at lower rates. When no more peroxide is left, O2 is no longer produced.

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