An Investigation of the Effect of Copper Sulphate on Catalase Activity.

Matthew Scott 04/11/01

An Investigation of the Effect of Copper Sulphate on Catalase Activity

Introduction

Catalase is an enzyme which catalyses the reaction between hydrogen peroxide (H2O2) is broken down into oxygen (O2) and water (H2O).

catalase

2H2O2 2H2O + O2

The heavy metal ions Cu+2 in copper sulphate inhibit this reaction. Copper sulphate is an irreversible non-competitive inhibitor.

Scientific Knowledge

Five main factors effect enzyme controlled reactions. They are: temperature; pH; substrate concentration; enzyme concentration; and, whether or not inhibitors are present. Therefore to investigate the effect of copper sulphate on catalase activity the temperature, pH, substrate concentration and enzyme concentration must be kept constant throughout the experiment. The factor to be investigated is the addition of inhibitors as it is the only factor to be varied.

Enzymes are protein molecules, which act as biological catalysts. They contain an active site to which a molecule or molecules can bind. This molecule is known as the substrate of the enzyme. While bound to the active site (by temporary bonds formed between some R groups of the enzyme’s amino acids, and the substrate), bonds are broken or formed in the substrate molecule and a product or products leave the active site. This is shown in Figure 1.

Figure 1. A simplified diagram to show the function of an enzyme.

Each enzyme is specific to one substrate as their active sites are shaped to enable one shape of the molecule to fit.

The addition of certain molecules to this process can prevent it from taking place. This reduces the rate of an enzyme controlled reaction. Such molecules are known as inhibitors. There are two types of inhibitors: competitive; and, non-competitive.

Competitive inhibitors are similar in structure to the substrate so compete with the substrate for the active site. They can fit into the active site and form an enzyme inhibitor complex so the substrate is unable to enter the active site. This is shown in Figure 2.

Figure 2. A simplified diagram to show the effect of a competitive inhibitor on the function of an enzyme.

The concentrations of substrate and inhibitor have an effect on the rate of reaction. The molecule which is in the highest concentration will be the one most likely to form a complex with the enzyme. If the substrate concentration is increased, the level of inhibition is decreased. So when the substrate concentration is high the inhibitor can have very little effect on the rate of reaction because the relatively larger number of substrate molecules overwhelms the inhibitor molecules. See figure 3.

Figure 3. A graph to show the effect of substrate concentration on the rate of a reaction with and without an inhibitor.

Competitive inhibitors have no permanent effect. They are reversible. The inhibition they cause can be removed and the reaction can continue. This is done by increasing the concentration of substrate or decreasing the concentration of inhibitor.

Non-competitive inhibitors are not similar in structure to the substrate so do not inhibit by taking the substrates place in the active site. The inhibitor combines with the enzyme molecule in a place other than the active site, which alters the structure of the enzyme. This has an effect on the shape of the active site so that the substrate is unable to bind with the enzyme and the rate of reaction is reduced. See Figures 4 and 5. The most common type of non-competitive inhibitors contain heavy metal ions. Examples include, mercury (Hg2+), silver (Ag+), and copper (Cu2+). Cu2+ is found in copper sulphate. It is Cu2+ which binds with the catalase molecule in one place and alters its structure and properties in another area on the protein. This is known as an allosteric effect.

Figure 4. A simplified diagram to show the effect of a non-competitive inhibitor on the function of an enzyme. This is the process that occurs when the substrate is hydrogen peroxide, the enzyme is catalase and the inhibitor is copper sulphate.

Unlike competitive inhibitors, non-competitive inhibitors are not affected by substrate concentration because increasing the concentration of substrate molecules does not affect the inhibitors ability to join to the enzyme. This means that a non-competitive inhibitor will always reduce the rate of reaction even if the substrate concentration is high.

Figure 5. A graph to show the effect of substrate concentration on the rate of reaction with and without a non-competitive inhibitor.

Prediction

I predict that adding copper sulphate to catalase will slow down the rate at which hydrogen peroxide is broken down into water and oxygen. There will therefore be more oxygen produced when copper sulphate is not present. I believe this because copper sulphate will act as a non-competitive inhibiter in the reaction.

I predict that the reaction will not continue when the concentration of hydrogen peroxide is increased at the end of the experiment. This is because copper sulphate contains the heavy metal ion Cu2+. Heavy metal ions act as irreversible inhibitors (as stated in the ...

An Investigation of the Effect of Copper Sulphate on Catalase Activity.

Matthew Scott 04/11/01