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ENZIM(LANJUTAN)

17 OKTOBER 2011

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SEJARAH PENEMUAN ENZIM DAN

ETIMOLOGI ENZIM

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Contoh-contoh nomor EC untuk enzim

Esterase = peroksidase =

Peptidase = reduktase =

Amilase = xantin oksidase =

Fosfatase = as.amino oksidase =

Lipase = glisin oksidase =

Dehidrogenase =

Oksidase =

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OXIDOREDUCTASE:Oxidizing or reducing a compound/

Transfering electron to or from a compound

SUCCINATE

C O

OH

CH2

CH2

C O

HO

SUCCINATE

DEHYDROGENASE

C O

OH

CH

CH

C O

HO

FUMARATE

FAD FADH2

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H OH

HYDROLASE:

Lysing a compound with the help of water

O

C

CC

C

C

CH2OH

H

OH OH

H OH

OH

H

H

HO

C

CC

C

C

CH2OH

H

OH

H OH

OH

H

H

HO

C

CC

C

C

CH2OH

H

OH

H OH

OH

H

H

H

O

H2O

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TRANSFERASE:

Transfering a functional group across molecules

COOH

C

CH2

COOH

H+H3N

L-ASPARTATE

COOH

COOH

-KETO

GLUTARATE

CH2

CH2

C O

+

COOH

CH2

COOH

L-GLUTAMATE

C O

OXALOACETATE

C H+H3N

COOH

COOH

CH2

CH2+

ASPARTATE

TRANSAMINASE

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ISOMERASE:

Transfering a functional group within a molecule

D-GLUCOSE 6-PHOSPHATE

C

C O

H

C

C

CH2

C

OHH

OHH

OHH

HHO

O PO4

C

O

C

C

CH2

C

OHH

OHH

HHO

CH2OH

O PO4

D-FRUCTOSE 6-PHOSPHATE

PHOSPHOGLUCO

ISOMERASE

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LYASE:

Cleaving an organic bond within a molecule

ISOCITRATE

COOH

COOH

CH2

HC

CHHO

COOH

SUCCINATE

CH2

CH2

COOH

COOH

+COOH

HC O

GLYOXILATE

ISOCITRATE

LYASE

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LIGASE:Formation of new organic bonds

OH

O

CH2

C

H

C

OH

H

C

H

C

OH

H

OPHO

O

LIGASE

OCH2

C

H

C

OH

H

C

H

C

OH

H

OH

OP

O

OH

OPO

OH

OPHOO

+

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LIGASE:Formation of new organic bonds

OH

O

CH2

C

H

C

OH

H

C

H

C

O

H

OPHO

O

OCH2

C

H

C

OH

H

C

H

C

OH

H

OP

O

HO

OH

PO

OH

OPHO

O

OH+

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Enzim

(holoenzim)

Protein

(apoenzim)

Bukan Protein(gugus prostetik)

Koenzim (organik)

Kofaktor

(Anorganik)

Ex: NADH, FADH, koenzim A,dan vitamin B. Ex: Fe

2+

, Cu

2+

, Zn

2+

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CofactorsCofactors may be one of three types1. Coenzyme: A non protein organic substance

that is loosely attached to the enzyme

2. Prosthetic Group: A non protein organicsubstance that is firmly attached to the

enzyme

3. Metal ion activators: K+, Fe2+, Fe3+, Cu2+,Co2+, Zn2+, Mn2+, Mg2+, Ca2+, or Mo2+,

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Types of Cofactors

Enzymes have varying degrees of specificity.

One cofactor may serve many different enzymes.

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Enzyme Specificity

The action of an enzyme depends primarily onthe tertiary and quaternary structure of theprotein that constitutes the enzyme.

The part of the enzyme structure that acts onthe substrate is called the active site.

The active siteis a pocket in the enzyme

structure where the substrate can bind.

1

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Active Site A restricted region of an enzyme

molecule which binds to the

substrate.

EnzymeSubstrate

ActiveSite

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How enzymes act as catalyst

General Principles: The Induced Fit Model

The lock-and-key model: proposed by Emil Fischer in

1894

The induced fit model: proposed by Daniel Koshlandin 1958, an enzyme induces a bound substrate molecule

to adapt a conformation resembling the transition state

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The Lock and Key Hypothesis

Fit between the substrate and the active site of the enzyme isexact

Like a key fits into a lock very precisely

The key is analogous to the enzyme and the substrateanalogous to the lock.

Temporary structure called the enzyme-substrate complexformed

Products have a different shape from the substrate

Once formed, they are released from the active site

Leaving it free to become attached to another substrate

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Enzyme maybe used again

Enzyme-

substratecomplex

E

S

P

E

E

P

Reaction coordinate

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This explains enzyme specificity

This explains the loss of activity when

enzymes denature

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SPECIFIC

+ NH4+

ASPARTASE

COOH

C

C

COOH

H

H

FUMARATE

COOH

C

C

COOH

H

H

MALEATE

ASPARTASE

COOH

C

CH2

COOH

H+H3N

L-ASPARTATE

COOH

C

CH2

COOH

H NH3+

D-ASPARTATE

ASPARTASE

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The Induced Fit Hypothesis

Some proteins can change their shape(conformation)

When a substrate combines with an enzyme, it

induces a change in the enzymes conformation The active site is then moulded into a precise

conformation

Making the chemical environment suitable for thereaction

The bonds of the substrate are stretched to make thereaction easier (lowers activation energy)

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The Induced Fit Hypothesis

This explains the enzymes that can react with a

range of substrates of similar types

Hexokinase (a) without (b) with glucose substratehttp://www.biochem.arizona.edu/classes/bioc462/462a/NOTES/ENZYMES/enzyme_mechanism.html
http://www.biochem.arizona.edu/classes/bioc462/462a/NOTES/ENZYMES/enzyme_mechanism.htmlhttp://www.biochem.arizona.edu/classes/bioc462/462a/NOTES/ENZYMES/enzyme_mechanism.html

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Enzymes and Reaction Rates

Factors that influence reaction rates of

Enzyme catalyzed reactions include

1. Enzyme and substrate concentrations2. Temperature

3. pH

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SUBSTRATE CONCENTRATION

At low concentrations, anincrease in substrateconcentration increases the

rate because there are manyactive sites available to beoccupied

At high substrateconcentrationsthereaction rate levels offbecause most of the activesites are occupied

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Substrate concentration

The maximumvelocityof a reaction isreached when the

active sites are almostcontinuously filled.

Increased substrateconcentration after thispoint will not increasethe rate.

Vmaxis the maximumreaction rate

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Substrate concentration

Vmaxis the maximumreaction rate

The Michaelis-Menten constant,K

m

is the substrateconcentration whenthe rate is Vmax

Kmfor a particular

enzyme with aparticular substrate isalways the same

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Enzyme KineticsKm reflects the affinity of the enzyme for the

substrate.

a) small km: reflects a high affinity of the enzyme for thesubstrate

b) large km: reflects a low affinity of the enzyme for thesubstrate

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Persamaan Michaelis-Menten

Vmax [S]

V= ----------

Km

+ [S]

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Michaelis-Menten Kinetics

if [S] > Km , vo = Vmax

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Example 1

The rate of an enzyme catalyzed reaction is 35mol/min at [S] = 10-4 M, (KM = 2 x 10

-5).

Calculate the velocity at [S] = 2 x 10-6

M.

Work the problem(alias dikerjakan donk)

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Example 2

Ten micrograms of carbonic anhydrase (MW =30000) in the presence of excess substrate exhibitsa reaction rate of 6.82 x 103mol/min.

At [S] = 0.012 M the rate is 3.41 x 103mol/min.

a. What is Vmax ?b. What is KM ?

Work these..

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RateofReaction

Enzyme Concentration

(HOW ?????)

Enzyme Concentration

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Effect of Temperature

Higher temperatureincreases the number ofeffective collisions and

therefore increases therate of a reaction.

Above a certaintemperature, the rate

begins to declinebecause the enzymeprotein begins todenature

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RateofReaction

Temperature

0 20 30 5010 40 60

40o

C - denatures

5- 40oC

Increase in Activity

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Effect of heat on enzyme activty

If you heat the protein above its optimal temperature

bonds break meaning the protein loses it secondary and tertiary

structure

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Effect of heat on enzyme activty

Denaturing the protein

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Effect of heat on enzyme activity

Denaturing the proteinACTIVE SITE CHANGES SHAPE

SO SUBSTRATE NO LONGER FITS

Even if temperature loweredenzyme cant regain its correct shape

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The effect of temperature

For most enzymes the optimum temperature is about

30C

Many are a lot lower, cold water fish will die at

30C because their enzymes denature

A few bacteria have enzymes that can withstand very

high temperatures up to 100C

Most enzymes however are fully denatured at 70C

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Effect of pH Each enzyme has an optimal

pH at which it is mostefficient

A change in pH can alter theionization of the R groups ofthe amino acids.

When the charges on theamino acids change,hydrogen bonding withinthe protein molecule changeand the molecule changes

shape.

The new shape may not beeffective.Pepsin is most efficient at pH 2.5-3

while Trypsin is efficient at a much

higher pH 46

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The effect of pH

Extreme pH levels will produce denaturation

The structure of the enzyme is changed

The active site is distorted and the substratemolecules will no longer fit in it

At pH values slightly different from the enzymes

optimum value, small changes in the charges of the

enzyme and its substrate molecules will occur This change in ionisation will affect the binding of

the substrate with the active site.

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Inhibitors

Inhibitors are chemicals that reduce the rate of

enzymic reactions.

The are usually specific and they work at lowconcentrations.

They block the enzyme but they do not

usually destroy it. Many drugs and poisons are inhibitors of

enzymes in the nervous system.

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The effect of enzyme inhibition

Irreversible inhibitors: Combine with the

functional groups of the amino acids in the

active site, irreversibly.Examples: nerve gases and pesticides,

containing organophosphorus, combine with

serine residues in the enzyme acetylcholine

esterase.

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The effect of enzyme inhibition

Reversible inhibitors: These can be washed

out of the solution of enzyme by dialysis.

There are three categories :Kompetitif

Non kompetitif

Un kompetitif

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Competitive Inhibitors

Competitive inhibition

occurs when the

substrate and a substance

resembling the substrateare both added to the

enzyme.

The inhibitor blocks the

active site on the enzymestopping its catalytic

action

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Competitive Inhibition

Compete foractive siteInhibitor

Substrate

CartoonGuide

EquationandDescription

[I] binds to free [E] only,

and competes with [S];

increasing [S] overcomes

Inhibition by [I].

E + SESE + P

+I

EI

E

I

S

Vmax

KmKm [S], mM

vo

I

Vmax unchangedKm increased

I

1/[S]1/Km

1/vo

1/Vmax

Intersectat Y axis

Vo/2

DirectPlots

DoubleRec

iprocal

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Non-competitive Inhibitors Non-competitive

inhibitors deactivate

the active site of the

enzyme.

They alter the enzyme

so that it can no

longer bind to thesubstrate

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Non-competitive Inhibition

CartoonGuide


DirectPlots

DoubleRec

iprocal

S

S E

Different site

[I] binds to free [E] or [ES]

complex; Increasing [S] can

not overcome [I] inhibition.

E + SESE + P

+ +I I

EI+SEIS

Km

Vmax

[S], mM

vo

I

Vmax

Vmax decreasedKmunchanged

I

Intersectat X axis

1/vo

1/Vmax

1/[S]1/Km

=Km

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Uncompetitive Inhibition

CartoonGuide


DirectPlots

DoubleRec

iprocal

I

I

S

S

E

[I] binds to [ES] complex

only, increasing [S] favors

the inhibition by [I].

E + SESE + P

+I

EIS

Km [S], mM

Vmax

I

Km

Vmax

Both Vmax & Kmdecreased

I

Two parallellines

1/[S]1/Km

1/Vmax

1/vo

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Type of reaction Effect of inhibitor

None None

Competitive Increases Km

Uncompetitive Decreases Km and Vmax

Noncompetitive (mixed) Decreases Vmax

(may increase or decrease Km)

Enzyme Inhibition (Summary)

75911036-enzim-2

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