1. Aspirin Inhibits Cycloxygenase
Chapter 22
Enzymes
Cyclooxygenase
Aspirin Inhibits Cycloxygenase

2. Work by speeding up reactions
i.e. lowering activation Energy (Ea). . .
Enzymes

3. Enzyme Catalysis Enzyme: a biological catalyst.
~all enzymes are proteins.
increase rate of a reaction by over vs uncatalyzed reaction.
Some catalyze the reaction of only one compound.
Some are stereospecific; for example, enzymes that catalyze the reactions of only L-amino acids (natural).
Some catalyze reactions of specific types of compounds or bonds;
e.g. trypsin catalyzes hydrolysis of peptide bonds of Lys and Arg.

4. Classification of Enzymes
Enzymes are commonly named after the reaction or reactions they catalyze.
example: lactate dehydrogenase, alchohol dehydrogenase.
Enzymes are classified into six major groups.
Oxidoreductases: oxidation-reduction reactions.
Transferases: group transfer reactions.
Hydrolases: hydrolysis reactions.
Lyases: addition of groups to a double bond, or removal of groups to create a double bond.
Isomerases: isomerization reactions.
Ligases: the joining to two molecules.

5. Classification of Enzymes
1. Oxidoreductase:
2. Transferase:
3. Hydrolase:

6. Classification of Enzymes
4. Lyase:
5. Isomerase:
6. Ligase:

7. Terms in Enzyme Chemistry
Apoenzyme: the protein part of an enzyme.
Cofactor: a nonprotein portion of an enzyme,
e.g. Zn2+ and Mg2+, Fe2+.
Coenzyme: a nonprotein organic molecule,
frequently a B vitamin,
that acts as a cofactor.
Substrate: the compound(s) whose reaction
an enzyme catalyzes.
Active site: portion of enzyme which a
substrate binds during reaction.

8. Terms in Enzyme Chemistry
1. Activation: any process that initiates or increases the activity of an enzyme. ( changes in [substrate] temperature, pH)
2. Inhibition: process that makes active enzyme less active / inactive.
3. Competitive inhibitor: substance that binds to active site of enzyme preventing binding of substrate.
4. Noncompetitive inhibitor: substance that binds to the enzyme other than active site  inhibits the activity.
3. Competitive inhibitor:
4. Noncompetitive inhibitor:

9. 4. Noncompetitive inhibitor:
Challenge Question
What is the difference between reversible and
Irreversible non competitive inhibition?
4. Noncompetitive inhibitor:

10. Enzyme Activity a measure of how much a reaction rate is increased.
We examine how the rate of an enzyme-catalyzed reaction is effected by:
enzyme concentration
substrate concentration
temperature pH

11. Enzyme Activity
Figure 22.3 The effect of enzyme concentration on the rate of an enzyme-catalyzed reaction. Substrate concentration, temperature, and pH are constant.
Each factor in:
1:1:1:1 ratio. . .
Linear growth!

12. 2:1 Substrate/Enzyme, excess substrate. . .
Enzyme Activity
Figure 22.4 The effect of substrate concentration on the rate of an enzyme-catalyzed reaction. Enzyme concentration, temperature, and pH are constant.
2:1 Substrate/Enzyme, excess substrate. . .
RXN slows
START
1:1 Substrate/Enzyme

13. Enzymes have specific optimal Temperatures they react @
Enzyme Activity
Figure 22.5 The effect of temperature on the rate of an enzyme-catalyzed reaction. Substrate and enzyme concentrations and pH are constant.
Enzymes have specific optimal Temperatures they

14. Enzymes have specific optimal pH levels they react @
Enzyme Activity
Figure 23.6 The effect of pH on the rate of an enzyme-catalyzed reaction. Substrate and enzyme concentrations and temperature are constant.
Enzymes have specific optimal pH levels they

15. Confirming your knowledge
The activity of pepsin was measured at various pH values. When the temp, concentration of pepsin and substrate were held constant the following data was obtained: pH
Enzyme reaction Activity
1.0
0.5
1.5
2.6
2.0
4.8
3.0
4.0
0.4
5.0
0.0
What is the optimal pH?
Predict the activity of pepsin in the blood (physiological pH ~7.4)

16. Mechanism of Action Lock-and-key model of enzyme mechanism.
The enzyme is a rigid three-dimensional body.
The enzyme surface contains the active site.