ch12 enzymes

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