Catalase is an enzyme found in both animals and many kinds of protists. It catalyzes the reaction that converts hydrogen peroxide, which is harmful to an organism, into water and oxygen. ..One molecule of catalase is capable of breaking down forty million molecules of hydrogen peroxide per second. Catalase uses hydrogen peroxide as both a substrate and a hydrogen acceptor. The molecular weight of the catalase from Bos taurus liver is approximately 250,000 daltons, and is composed of 4 subunits of equal size. The optimal pH for the activity of this enzyme is approximately 7.0, which is close to the overall pH of Bos Taurus. Other pH levels which are either well above or well below optimal pH range will cause ionization of the enzyme, subsequently resulting in the denaturing of the enzyme itself. Furthermore, the optimal temperature for catalase activity is thought to be around 37°C, which is around the normal body temperature for Bos taurus. Temperatures below optimal temperature result in decreased molecular movement, thus reducing the collisions between catalase and its substrate which are necessary for catylization. Temperatures over the optimal temperature result in denaturing of the enzyme. Sunlight and lyophilization can also cause the catalase enzyme to become inactive.
	The effect of enzyme concentration on reaction rate can be summarized in the following graph
: 
	As enzyme concentration increases, the reaction rate will also increase.
	
	The question under examination was that of the effect of pH on the activity of catalase from the liver of Bos taurus. It was hypothesized that since the normal pH of Bos taurus is approximately 7.0, then the optimal pH for catalase activity would also be approximately 7.0.
	Materials necessary for the conduction of an experiment to test the experiment were a CBL system, TI graphing calculator, Vernier Biology Gas Pressure Sensor, Vernier DIN adapter cable, 1-hole rubber stopper assembly, 10 mL graduated cylinder, 250 mL beaker of water, solution of 3% hydrogen peroxide, 600 mL beaker, enzyme suspension, 4 18 x 150 mm test tubes, goggles, ice, pH buffers (pH4, pH7,  pH 10), test tube rack, thermometer, and three dropper pipettes. The data was collected with the bio-gas pressure probe attached to the CBL using the chem-bio program. Three clean test tubes were placed in a rack and labeled with pH 4, pH 7, and pH 10. Three mL of a solution of 3% H2O2 was then added to each test tube, followed by 3 mL of the pH buffer which corresponded to the pH on the labels of the test tubes. A pipette containing catalase from Bos taurus liver chilled in ice and in a styrofoam container was then obtained and two drops were added into the test tube labeled pH 4. The 1-hole stopper assembly was then firmly inserted into the test tube. The contents of the test tube were swirled, the air valve on the pressure sensor was then closed, pressure probe was triggered by pressing enter on the calculator. The pressure level was monitored to ensure that it would not exceed 1.3 atmospheres, which would result in the rubber stopper popping off. Had the pressure exceeded or met 1.3 atm, then the air valve on the pressure sensor would have been opened. After 3 minutes, the CBL screen displayed DONE, and the graph of the accumulated data was observed on the TI graphing calculator. The most linear region from the graph was taken; the first point of the region was recorded as the initial pressure and the initial time, and the last point was recorded as the final pressure and final time. This procedure was then repeated on the remaining test tubes.

	The results of the experiment were that the atmospheric pressure in the test tube labeled pH 7 increased the most rapidly. 
	
Test Tube     3% H2O2(mL)    buffer(mL)    Catalase(drops)   Time, Initial Pressure    Time, Final Pressure
pH4		3		3                     2
pH7		3		3	       2
pH 10		3		3	       2

	The subject under examination in this experiment was what was the effect of pH levels on enzyme activity. The formulated hypothesis was that since the pH in Bos taurus is approximately 7.0, then the optimal pH for catalase activity would also be approximately 7.0. It was predicted that the test tube with the greatest and fastest increase in atmospheric pressure was the one with the greatest rate of reaction. The test tube with the greatest and fastest increase of atmospheric pressure was the test tube containing a pH buffer of 7, thus, the test tube with optimal pH for the activity of catalase was a pH of 7.

pH	
		   pH 4		    pH 7		    pH 10
		5.00 * 10^-4	2.30*10^-3	5.00*10^-4
					
					Concentration
		  1 drop	   2 drops	  3 drops            4 drops
		2.19*10^-2	1.63*10^-2	1.71*10^-2	3.94*10^-3

Temperature
	  	    4°C	                 22°C	   37°C		   50°C
		-2.98 *10^-4	-2.64*10^-4	1.15*10^-3	1.10*10^-2

	The results of the experiment did support the proposed hypothesis and prediction. The optimal pH for enzyme activity was in fact that found in Bos taurus, a pH of 7.  This result supports what is already known through previous research and experimentation. Enzymes have an optimal pH level at which enzyme activity is the greatest. However, the results of the temperature experiment did not support the research. It was found that the reaction rate was greatest at a temperature of 50°C, not at a temperature of 37°C. The reaction rate should have increased as more enzyme was added,  but it appeared to decrease after the fourth drop of enzyme was added to the solution. This was most likely due to the fact that the reaction reached its feasible limit and thus leveled off.
	Several problems arose during the experiment itself. One such problem that may have caused error was that the time between putting the stopper onto the test tube and activating the CBL did not remain constant. This would  make the data collection inaccurate. Another problem we encountered was with the closing of the air valve. On one trial we neglected to close the air valve and thus recorded a constant room pressure instead of the pressure inside of the room. 
	The conditions optimal for enzyme activity are those which closely match the conditions of its normal surroundings. The conditions optimal for the activity of the enzyme catalase were those which closely matched the conditions found in Bos taurus.

Works Referenced
“Catalase” <http://www.worthington-biochem.com/manual/C/CTL.html#Schroeder>.

“CELLS AND BIOMOLECULES 1 CELLULAR SYSTEMS ENZYMES, COENZYMES 	AND 
ATP”  <http://fhis.gcal.ac.uk/BIO/micro/drjrattray/cab1lec.summ /enzyme.  	html>.

“Enzyme Inhibition and Regulation” <http://www.chem.wsu.edu/Chem102/102- 	EnzInhibReg.html>.

“Enzymes”. <http://www.ultranet.com/~jkimball/BiologyPages/E/Enzymes.html>.

The Effect of pH on Catalase Activity
Mark Cruz

IB Biology
Mrs. Meyer
10/25/01