ch12 enzymes
TRANSCRIPT
Introduction to Enzymes(Chapter 12)
Department of Biochemistry and Molecular Biology
LSUMC Shreveport, La
Enzymatic Catalysis Suited to Biological systems
Higher reactions rates Milder reaction conditions Greater reaction specificity Capacity for regulation
Enzyme-substrate interactions-a prerequisite for catalysis
Forces Important for substrate recognition
Active Site Characteristics
LOCK AND KEY INDUCED FIT
Models for Enzyme Substrate Interactions
Carboxypeptidase A-Substrate Induced Changes in Active Site Conformation
N
N
N
H
2 O
OO
O
N
N
CH
H2
H H
H
P
O
O
O
P
O
O
O
P
O
O
O
-
- - -
ATP
Enzyme Cofactors
+
N
H
2 O
OO
O CH
H H
H
P
O
O-
N
N
N
H
2 O
OO
O
N
N
CH
H2
H H
H
P
O
O-
O
O
C-NH2
H
+N
H
2 O
OO
O CH
H H
H
P
O
O-
N
N
N
H
2 O
OO
O
N
N
CH
H2
H H
H
P
O
O-
O
O
C-NH2
H H
+ H + 2e+ -
-- H - 2e
..
NAD NADH+
Enzyme Cofactors
HS-CH -CH -N-C-CH -CH -N-C-C-C-CH-
N
N
N
H
2 O
OO
ON
N
CH
H2
H H
H
P
O
O-
OP
O
O22
O
H
CoASH
O
-
2
O OH
H
CH3
CH3
2H
2
Enzyme Cofactors
23 3
ALCOHOL DEHYDROGENASE
CH -CH -OH + NAD CH -CH=O + NADH + H+ +
Enzyme Classifications
Oxido-reductases
Transferases
Enzyme Classifications
Hydrolases
PROTEASE
R-NH -CH-C-NH-CH-C-NH-R
OO
R R1 2
+ H O2
R-NH-CH-C-OH
R1
O
NH -CH-C-NH-R2
R2
O
+
Lyases
ENOLASE
O
O
O P-
-
CH -OH
O-C-H
C-O
O
- O
O
O P-
- C-O
O
2
-
CH
O-C + H O2
2
Enzyme Classifications
Isomerases
Ligases
Enzymatic Reactions of High Structural Specificity Hydrolysis
Enzymatic Reactions of High Structural Specificity Isomerization
(CH ) -CH23 O (CH ) -CH
23OH
ADH
H + NADH NAD+ +
CH -CH CH -CH -OHO3
ADH
H + NADH NAD+ +
3 2
Enzymatic Reactions of Low Structural Specificity Oxidation-Reducton
CO H
C
H N
2
CH3H
CO H
CHN
2
CH3H
D-ALANINE
L-ALANINE
3
3
+
+
CO H
C
2
CH3
O + NH +
4
D-AMINO ACID OXIDASE
Enzymatic Reactions with Stereochemical Specificity
23 3
ALCOHOL DEHYDROGENASE
CH -CH -OH + NAD CH -CH=O + NADH + H+ +
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
Enzyme regulation by metabolic end products