Catalase is an enzyme found in the cells of animals, plants and aerobic bacteria. An enzyme is a large organic molecule synthesised in cells and made to act as a catalyst in a reaction. Each type of enzyme performs a specific function, and the function of catalase is to convert a potentially harmful by-product into usable elements.
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Catalase, like most enzymes, is a protein. It is found in perixisomes, which are membrane-bound organelles of cells. Catalase has an important biological function: it catalyses the breakdown of hydrogen peroxide, a toxic substance to organisms, to water and molecular oxygen, which are both harmless and useful.
Catalase is a dumbbell shaped structure with four polypeptide chains, each containing over 500 amino acids. Catalase also has four heme groups, which are made up of protoporphyrin rings containing a single iron atom. These rings are nestled within the four chains.
The Importance of Catalase
Hydrogen peroxide is a by-product of many biological functions of organisms. All aerobic organisms use oxygen for respiration. The reduction of oxygen into water is sometimes incomplete, and an extra electron from a metal ion can be transferred, causing the formation of peroxide. However, most of the hydrogen peroxide is created during the production of ATP in the mitochondria.
Although peroxide is toxic to living cells, the reaction to break it back down to water and oxygen happens quickly and efficiently. Catalase is known as one of the most efficient enzymes, having a turnover number close to 200,000 events/second/subunit. Without catalase to increase the rate of the reactions, hydrogen peroxide would remain, damaging cells.
Factors Affecting the Activity of Catalase
Catalase and its rate of activity are affected by many factors, including temperature, pH, salt concentration, amount of substrate and the presence of inhibitors or activators.
Temperature is an important factor in all biochemical reactions, as high temperatures cause denaturation of enzymes. As the enzyme denatures, it changes the conformation, causing the substrate to bind less efficiently, therefore decreasing the reaction. However, until that maximum temperature (which is different for each type of catalase) is reached, the reaction will increase as the temperature increases.
The pH, the measure of acidity or hydrogen ion concentration with a solution, is measured on a scale of 0-14. As a solution becomes more acidic (below 7), the enzyme can gain a hydrogen ion from the solution and as the solution becomes more basic (above 7), it can lose a hydrogen ion. Either of these extremes can reduce the rate of the reaction as it changes the chemical bonds of the catalase.
There are two types of inhibitors: non-competitive inhibitors, which bind somewhere other than the active site, and competitive inhibitors, which bind to the active site of the catalase. Copper sulphate is a known non-competitive inhibitor of catalase, and cyanide is a known inhibitor.
In general, as the amount of hydrogen peroxide increases, the rate of the reaction will also increase. However, enzymatic reactions follow the Michaelis-Menten equation, which reflects that every reaction will reach a saturation point, meaning that at some maximum reaction rate, the addition of more substrate will cease to have an effect.
Other Uses of Catalase
Because catalase is present in just about all living organisms, it is one of the most studied enzymes. This has led to scientists finding other functions for this efficient enzyme. Catalase is used to treat the inside of food wrappers. The catalase prevents oxidation and therefore helps preserve the food. Catalase is also used during the process of cold sterilisation, which is a process to preserve milk and cheese by treatment with hydrogen peroxide. The catalase is used to remove any remaining traces of the hydrogen peroxide.
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