Aspirin Inhibits Cycloxygenase Chapter 22 Enzymes Cyclooxygenase Aspirin Inhibits Cycloxygenase

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

Enzyme Catalysis Enzyme: a biological catalyst. ~all enzymes are proteins. increase rate of a reaction by 109- 1020 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.

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.

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

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

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.

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:

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

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

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!

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

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 react @

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 react @

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)

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.