Enzyme Lab - Catalase Activity
Practically all of the numerous and complex biochemical reactions that take place in animals, plants, and microorganisms are regulated by enzymes. Most enzymes are Proteins. Each enzyme is able to promote only one type (or a small number) of chemical reaction. Enzymes can be classified into several broad categories, such as hydrolytic, oxidizing, and reducing, depending on the type of reaction they control. In an enzyme catalyzed reaction, the compounds on which the enzyme acts are called substrates and the resulting compounds are called products. Today, we will quantitatively investigate a reaction catalyzed by the enzyme Catalase.

The enzyme Catalase catalyzes the following reaction:

Put in words, Catalase takes two molecules of hydrogen peroxide (H₂O₂) and converts them to two water molecules plus a molecule of oxygen gas. Hydrogen peroxide is a toxic molecule (that's why we use it to kill Bacteria). However, H₂O₂ is frequently created in our bodies during normal metabolic events. To remove any unwanted H₂O₂ the enzyme catalase is present in the peroxisomes of nearly all human cells. There, it serves to protect the cell from any toxic effects by catalyzing the decompostion of H₂O₂ without the production of Oxygen free radicals.

The Catalase protein exists as a dumbbell-shaped tetramer of four identical subunits (220,000 to 350,000 kD). Each monomer contains a heme prosthetic group at the catalytic center. This is the same type of Heme group as found in Hemoglobin. In the middle of each heme group sits an iron atom. Catalase uses the iron atom to help it break the bonds in the two molecules of hydrogen peroxide, shifting the atoms around to release two molecules of water and a molecule of oxygen gas.

Temperature can directly affect the rate of an enzymatic reaction. Firstly, all chemical reactions are affected by temperature, according to the laws of thermodynamics. The increased molecular motion that occurs as a result of increased temperature, makes collisions between the Enzyme and substrate more likely, and therefore the reaction will occur at a greater rate.

So generally, as temperature increases so does the rate of reaction. However one must also bear in mind that high temperatures can cause thermal denaturation of the enzyme and freezing may also damage an enzyme. Denaturation is a change in the tertiary structure of an Enzyme. An enzyme's function is related to its 3-dimensional (Tertiary) structure. This structure can be altered by heat, thus causing the enzyme to lose function.

Enzyme activity can also be affected by pH. We will take advantage of this fact to "Stop" our reactions in order to take measurements. When you add the sulfuric acid to your catalase reactions you lower the pH below the range where catalase is functional, and the reaction stops. In the case of catalase, the optimum pH is approximately pH 7.0. That is, catalase works best at a neutral pH. If the solultion is too acidic (low pH value) or too basic (high pH value) the catalase is inactive - no longer functions as an enzyme.

More