1. Introduction to Enzymes
Department of Biochemistry and Molecular
Biology
LSUMC Shreveport, La

2. Enzymatic Catalysis Suited to
Biological systems
Higher reactions rates
Milder reaction conditions
Greater reaction specificity
Capacity for regulation

3. Enzyme-substrate interactions-a
prerequisite for catalysis
Forces Important for
substrate recognition
Active Site
Characteristics

4. Models for Enzyme Substrate Interactions
LOCK AND KEY INDUCED FIT

5. Carboxypeptidase A-Substrate Induced
Changes in Active Site Conformation

6. Enzyme Cofactors
N
N
N
H
2 O
O O
O
N
N
CH
H2
H
H H
O
P
O
O
O
P
O
O
O
P
O
O
-
- - -
ATP

7. Enzyme Cofactors
+
N
O CH
H
2 O
H O O
H
H
O
P
-O
N
N
N
H
2 O
O O
O
N
N
CH
H2
H
H H
P
O
- O
O
O
C-NH2
H
+ N
O CH
H
2 O
H O O
H
H
O
P
-O
N
N
N
H
2 O
O O
O
N
N
CH
H2
H
H H
P
O
- O
O
O
C-NH2
H H
+ H + + 2e -
- H - 2e-
..
+
NAD NADH

8. HS-CH -CH -N-C-CH -CH -N-C-C-C-CH-N
N
N
H
2 O
O O
O
N
N
CH
H2
H
H H
O
P
O
-
O
P O
O
2 2
O
H
CoASH
O
-
2
O O H
H
CH3
CH3
2
H
2
Enzyme Cofactors

9. Enzyme Classifications
Oxido-reductases
CH -CH -OH + NAD+ CH -CH=O + NADH + H+
3 2 3
ALCOHOL DEHYDROGENASE
Transferases

10. Enzyme Classifications
Hydrolases
PROTEASE
O O
R-NH -CH-C-NH-CH-C-NH-R
R1 R2
+ H O 2 R-NH-CH-C-OH
R1
O
NH2 -CH-C-NH-R
R2
O
+
Lyases
-O P
ENOLASE
O
-O P
O
-
CH -OH
O-C-H
C-O
O
O
- O
CH
O-C + H O
- C-O
O
2
-
2
2

11. Enzyme Classifications
Isomerases
Ligases

12. Enzymatic Reactions of High Structural Specificity
Hydrolysis

13. Enzymatic Reactions of High Structural Specificity
Isomerization

14. Enzymatic Reactions of Low Structural Specificity
ADH
(CH3 ) 2-CH O (CH ) -CH 3 2 OH
+ +
H + NADH NAD
ADH
CH3 -CH O CH -CH -OH
+ +
H + NADH NAD
3 2
Oxidation-Reducton

15. Enzymatic Reactions with Stereochemical
CO H
2
C
+
NH
H3C H
D-ALANINE
CO H
C
+
H N
3
2
CH3
H
3
L-ALANINE
CO 2
H
C
CH3
O + NH
+
4
Specificity
D-AMINO ACID OXIDASE

16. CH -CH -OH + NAD+ CH -CH=O + NADH + H+
3 2 3
ALCOHOL DEHYDROGENASE

18. Catalytic vs Binding Specificity
As opposed to lock and key model, enzyme
recognizes and binds transition state, better than
substrate
For enzymes recognizing a variety of structurally
similar substrates, the tighter binding substrates
often are catalyzed to product slower than weaker
binding substrates

19. Enzyme regulation by metabolic end products