Catalase as a Model for Enzyme Catalysis and Reaction Rate
Abstract:
Introduction: Metabolism is the sum of chemical reactions occurring within an organism
or a cell (Losos pg G-13). These reactions include a host of processes from simple reactions
to complex biochemical pathways. Although these reactions can occur spontaneously, they
occur too slowly for the products to be efficiently utilized by the cell. To survive, cells rely
on enzymes to catalyze reactions. In essence, an enzyme is generally a protein that
catalyzes or increases the rate of a chemical reaction. Enzymes bind to substrates at active
sites. The individual amino acids of an enzyme result in specificity for one type of
substrate. Shape of an enzyme also determines which substrates it is capable of bonding
with. The fit is not perfect and small changes of the active site occur when it bonds to a
substrate. This is known as induced fit. (Holtzclaw pg 3-5) Despite this change, enzymes
do return to their original shape and are able to be reused over and over again. (Lab
Manual pg 19)
Enzymes will only function in optimal conditions. The salinity, pH, and temperature
are several factors that can cause a protein to denature, or unfold, rendering it inactive.
The presence of activators increases the rate of enzyme catalyzed reactions. Inhibitors do
the opposite by slowing or halting a chemical reaction. Both activators and inhibitors
allow the cell to control the rate at which chemical reactions occur. (Lab Manual pg 19-20)
The initial rate of an enzyme catalyzed reaction should be linear when graphed.
This is because with a large amount of substrate, there is a large amount of substrate to
enzyme contact. The rate of a reaction is based on this initial rate and can be calculated
by the equation  y /  x. This equation is the slope of the linear portion of the graph of
time vs. products. (Lab Manual pg 19-21)
Based on the above information we hypothesized the following; If the enzymes react with
the substrate for a longer time, then more substrate will be used up because the substrates
will be in contact with the enzymes longer thus creating more products.
Purpose: The first purpose of this experiment is to calculate effects of changes in
temperature, pH, enzyme and substrate concentration on enzyme catalyzed reaction rates
and to understand how these changes affect the reaction rates. The second purpose is to
calculate the rate of reaction of hydrogen peroxide with catalase. (Lab Manual pg 19)
Results:
Exercise 2B: The Base Line Assay

Table I: Base Line Calculation
Base Line Calculation
Final Reading of Burette
37.1 mL
Initial Reading of Burette
28.1 mL
Base Line (Final –Initial)
9 mL KMnO4
Exercise 2C: The Uncatalyzed Rate of H2O2 Decomposition

Table II: Uncatalyzed H2O2 Decomposition
Uncatalyzed H2O2 Decomposition
Final Reading of Burette
32 mL
Initial Reading of Burette
22.9 ml
Amount of H2O2 Spontaneously Decomposed (mL Baseline –
mL KMnO4)
-.1 ml
Percent of H2O2 That Spontaneously Decomposed in 24
Hours [(mL Baseline –mL 24 hours)/mL Baseline] X 100
-1.11%
Exercise 2D: An Enzyme-Catalyzed Rate of H2O2 Decomposition

Table III:
KMnO4 (ML)
Base Line
(mL)
Final
Reading
(mL)
10
9
32.8
Time (Seconds)
30
60
9
9
33
33.4
90
9
120
9
180
9
360
9
33.5
33.8
44.8
45.2
Initial
Reading
(mL)
Amount of
KMnO4
Consumed
Amount of
H2O2 Used

32
32.8
33
33.4
33.5
44.2
44.8
0.8
0.2
0.4
0.1
0.3
0.6
0.4
8.2
8.8
8.6
8.9
8.7
8.4
8.6
Graph I: Product Formed Individual Data
Product Formed (Individual Group Data)
12
R² = 0.1313
10
8.8 8.6 8.9 8.7
8.2
Product
8
8.6
8.4
Product Formed
6
Linear (Product Formed)
4
Linear (Product Formed)
2
0
0
0

100
200
Time (Seconds)
300
Graph II: Product Formed Class Data
400
Product Formed (Class Data)
12
Product Formed
10
9.4
8
9.3
9.7
9.4
R² = 0.8597
9.4
7.7
6
5.9
Series1
Poly. (Series1)
4
2
0
0
0
10
30
60
90
120
Time (Seconds)
180
360
References:
Losos, Jonathan B. et al. 2008. Biology, 8th ed. New York, New York: The McGraw-Hill
Companies, Inc
Lab Manual - LAB TWO Enzyme Catalysis
Holtzclaw, Theresa. "Enzyme Catalysis." The Biology Place. Person Education Inc, n.d. Web.
13 Oct. 2011. <http:/http://www.phschool.com/science/biology_place/
labbench/lab2/intro.html>.