EFFECTS OF PH ON ENZYME ACTIVITY
Purpose The purpose of this experiment was to study the effects of pH on catalase enzymeactivity. Introduction Every chemical reaction within the cell requires an enzyme to lower its activation energy. Even exergonic reactions happen too slowly to be useful without a catalyst. Almostall enzymes are proteins. To catalyze a reaction, the enzyme must interact with the reactant or reactants. This interaction takes place in a region of the enzyme called the active site. The reactant, or substrate for the enzyme, must fit perfectly into the active site of the enzyme in order for the enzyme to operate. Therefore, most enzymes are only able to catalyze a single chemical reaction. This is called specificity, and most enzymes are very specific (Cecamgmmacz, 2011). Under favorable conditions, the enzyme can operate with maximum efficiency, andthe chemical reaction occurs very rapidly. This is an enzyme’s optimum activity (Brooker,2011). Some environmental conditions, e.g. temperature and pH, can affect an enzymes activity. The concentration of enzyme or substrate can also have a dramatic effect on enzyme activity, and that is the variable studied in thisreport. [unique_solution]The enzyme being studied was called catalase, which was isolated from potato andliver. Its substrate is hydrogen peroxide, and its products are oxygen gas and water. In this experiment the behavior of the catalase enzyme was tested at a variety of different pHlevels. A neutral pH of 7 was used as the control environment because the enzyme would react favorably in this environment, since most living organisms (including potatoes) maintain a relatively neutral internal environment. • Catalase isolated from potatoes • Hydrogen peroxide • Water • HCl • NaOH Materials • Wax pencil • Metric ruler • Test tubes • Pipettes Methods Test tubes 1-3 were numbered and labeled at 1cm, 3cm, and 7cm from the bottomof the tube. Each was filled to the 1cm mark with potato juice (catalase). Tube 1 was filled tothe 3cm mark with HCl, tube 2 was filled to the 3cm mark with distilled water, and tube 3 wasfilled to the 3cm mark with NaOH. Each tube was then allowed to sit for 5 minutes atroom temperature. Then, one at a time, each tube was filled to the 7 cm mark with hydrogen peroxide and, after 20 seconds had elapsed, the bubble column height was measured and recorded. Tube 2 overflowed, so the height of the tube was recorded as the bubble column height for thatsample. Lab Report Materials – 33 – 0 0 Results The greatest enzyme activity was seen at pH 7, which had 120cm of oxygen bubbles. At pH 4, 0 cm of oxygen bubbles were measured and at pH 12, 0 cm of oxygen bubbles were measured. Height of Bubble Column in cm 14 12 12 10 8 6 4 2 0 pH ＝ 4 pH ＝ 7 pH ＝ 12 Height of Bubble Column in cm Discussion Only one tube, the tube at pH 7, had a measurable amount of oxygen bubbles,showing that the enzyme was active. Normal physiological pH is 7.4, so this tube was very close tothe normal pH of living cells. The enzyme catalase was able to work well under these conditions. At pH 4 and pH 12, the enzyme was not active. These extreme pH levels denatured the catalase, changing its shape so that it could not break down the hydrogen peroxide(Brooker, 2011). This experiment could have been improved by making it possible to measure smaller changes in pH. This would have allowed comparisons of pH values close to 7, such as 7.8 or7.3. Under these conditions, it would have been possible to determine exactly which pHchange inactivatesthe enzyme. Future experiments could include the one described above. Another similarexperiment could test other important enzymes such as proteases or lipases under different pHconditions. Another could test the enzymes found in the stomach, which are normally active at acidic pH values. The results seen here would predict that these enzymes would not be inactivated by acidity, but instead might be inactive at neutral pH. References Brooker, Robert, Eric Widmaier, Linda Graham, and Peter Stiling. (2011). An Introductionto Energy, Enzymes, and Metabolism. Biology 2nd Edition, 118-135. Cecamgmmacz. (14 July 2011). Enzymes activation energy [Video file]. Retrieved 2February from http://www.youtube.com/watch?v＝Dd1yi2aVoOc