Chem Lecture 4 Enzymes

Transcription

1 Chem Lecture 4 Enzymes Enzymes are biological catalysts. Nearly every reaction that takes place in a living cell is catalyzed by an enzyme. Most enzymes are proteins. Beside their role in speeding up the rates of chemical reactions, enzymes also play an important role in controlling the flow of material through the myriad of metabolic pathways required to sustain a living cell.

2 Enzyme Kinetics Most Reactions involve multiple substrates. There are three different ways that the binding substrates can occur. Ordered sequential Random sequential Double displacement (Ping Pong) 2

3 Enzyme Kinetics Ordered sequential 3

4 Enzyme Kinetics Random sequential 4

5 Enzyme Kinetics Double displacement (Ping Pong) 5

6 Enzyme Kinetics Not all enzyme obey the Michaelis- Menten model. 6

7 Enzyme Kinetics Not all enzyme obey the Michaelis- Menten model. 7

8 Enzyme Inhibition The inhibition of enzyme activitity can be physiological or not. It can be reversible or irreversible. Many drugs, pesticides and herbicides operate by inhibiting enzyme activity 8

9 Irreversible inhibition, while not usually physiological, can be used as a tool to study enzyme. Catalytic groups at the active site are often more reactive than groups elsewhere on the enzyme. Enzyme Inhi 9

10 Irreversible inhibition, while not usually physiological, can be used as a tool to study enzyme. Catalytic groups at the active site are often more reactive than groups elsewhere on the enzyme. DIPF is a powerful nerve gas toxin Enzyme Inhi 9

11 Irreversible inhibition, while not usually physiological, can be used as a tool to study enzyme. Catalytic groups at the active site are often more reactive than groups elsewhere on the enzyme. Enzyme Inhi 9

12 Irreversible inhibition, while not usually physiological, can be used as a tool to study enzyme. Catalytic groups at the active site are often more reactive than groups elsewhere on the enzyme. Bromoacetol phosphate is an affinity label which mimics the natural substrate for the enzyme triosephosphate isomerase Enzyme Inhi 9

13 Irreversible inhibition, while not usually physiological, can be used as a tool to study enzyme. Catalytic groups at the active site are often more reactive than groups elsewhere on the enzyme. Enzyme Inhi 9

14 Suicide inhibitors of monoamine oxidase (MAO) Irreversible inhibition, while not usually physiological, can be used as a tool to study enzyme. Catalytic groups at the active site are often more reactive than groups elsewhere on the enzyme. Enzyme Inhi 9

15 Irreversible inhibition, while not usually physiological, can be used as a tool to study enzyme. Catalytic groups at the active site are often more reactive than groups elsewhere on the enzyme. Suicide inhibitors of monoamine oxidase (MAO) (-)Deprenyl Enzyme Inhi 9

16 Irreversible inhibition, while not usually physiological, can be used as a tool to study enzyme. Catalytic groups at the active site are often more reactive than groups elsewhere on the enzyme. Enzyme Inhi 9

17 Enzyme Inhibition Reversible inhibition comes in three different forms. Competitive Noncompetitive Uncompetitive Enzyme kinetics can be used to distinguish between these. 10

18 Enzyme Inhibition Competitive Inhibition 11

19 Enzyme Inhibition Competitive Inhibition 12

20 Enzyme Inhibition Competitive Inhibition K M app = K M [ 1+ I ] K I 13

21 Enzyme Inhibition Competitive Inhibition 14

22 Enzyme Inhibition Competitive Inhibition K M app = K M [ 1+ I ] K I 15

23 Enzyme Inhibition Competitive Inhibition 16

24 Enzyme Inhibition Noncompetitive Inhibition 17

25 Enzyme Inhibition Noncompetitive Inhibition V app MAX = app V MAX [ 1 + I ] K I 18

26 Enzyme Inhibition Noncompetitive Inhibition 19

27 20 Enzyme Inhibition Uncompetitive Inhibition 20

28 20 Enzyme Inhibition Uncompetitive Inhibition 21

29 Enzyme Inhibition Uncompetitive Inhibition Both K M and V max are affected to the same extent 22

30 Problem C) Ibuprofen is an inhibitor of the enzyme prostaglandin endoperoxide synthase. By inhibiting the synthesis of prostaglandins, ibuprofen reduces both inflammation and pain. Using the data below, determine the type of inhibition that ibuprofen exerts on prostaglandin endoperoxide synthase [S] {mm} vo {mm/min} vo {mm/min} /w Ibuprofen

31 Enzyme Inhibition Some inhibitors are transition state analogues instead of substrate analogues. 24

32 Synthetic Enzymes Antibody enzymes (Abzymes) Antibodies raised to transitions state analogues exhibit enzymatic activity Antibodies raised to this compound have ferrochelatase activity ( 2,500 x the uncatalyzed reaction) 25

33 Enzyme Classification Enzymes are classified based on the types of reactions they catalyze Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB) 26

34 Next up Catalytic Strategies (Chapter 9) Protease reaction (Hydrolysis rxn) Carbonic anhydrase (Hydration rxn) Restriction endonuclease (Hydrolysis rxn) Myosin ATPase 27