inhibition -robin1 2003

8/4/2019 Inhibition -Robin1 2003

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Any substance that can diminish or slow down ordecrease the activity of enzyme is called inhibitor andthe process is called inhibition


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CONTENTS1.DEFINATION

2.TYPES OF INHIBITION

a. Reversible Inhibition b. Irreversible Inhibition

c. Allosteric Inhibition


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2.


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I. Define :

In Reversible inhibition the inhibitors bind to the

enzyme through non covalent bonds


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In this the chemical structure of inhibitor closelyresembles that of substrate

It binds to the enzyme at the substrate binding siteforming an EI complex rather than ES complex


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NOTE

Km value is increased, but the Vmax remainssame.

S E+ S E E + P

EI I E PE +

NOTE


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As the Inhibitor is structurally similar tosubstrate

Due to which they will compete for thesame binding site.

Affinity of the substrate for the enzymeprogressively decreases with increase in

concentration of inhibitor

Increase in concentration of substratewill make the inhibitor reversible


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The inhibitor bind at a site other than active site on

the enzyme surface


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At a slower

rate

+

IE

E

+S

E I S

E SE P

+ PE

+S

NOTEVmax decreases ,but no effect on Km


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I. Define :

In Irreversible inhibition the inhibitors bind to the

enzyme through covalent bonds.


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a) DIFP OH group serine

Ach Acetate + Choline

b) IodoacetateSH group of cystine

And imidazole group of histidine

Acetyl choline esterase


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MEAN

Allo = other

Steros =space The enzyme have a catalytic site as well as extra

allosteric site for binding regulatory metabolite whichis called as a modulator.


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Examples of allosteric inhibition1. Carbamyl + aspartate carbamyl

aspartate CTP( -ve modifier)

1. Hexokinase: activator ADP, Inhibitor :ATP

2. Phosphofrutokinase: activator AMP ,Inhibitor: ATP

Aspartate carbamylase

ATP(+ve modifier)


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Activity of an enzyme is enhanced or sometimeslowered by certain metabolic intermediates(allosteric modifiers)

Modifiers binds to the allosteric site and inducesconformation changes at the active site ,so that theenzyme activity is accerlated or reduced


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Modulator There are two types of modulator

1)Positive modulator= increases the enzyme activity

2)Negative modulator=inhibit the enzyme activity


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In multienzyme system the first enzyme of thesequence is the regulatory enzyme.

The end product inhibits the enzyme when profusedin excess concentration.


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In multienzymesystem the first enzyme

of the squence is theregulatory enzyme.

The end product

inhibits the enzymewhen profuced inexcess concentration.

Glycine +Succinyl CoA

ALA

heme

ALA Synthase

-vemodifier


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Importance of inhibition1.) Chemotherapy

The most common uses for enzyme inhibitors are as drugs totreat disease. Many of these inhibitors target a humanenzyme and aim to correct a pathological condition.However, not all drugs are enzyme inhibitors. Some, suchas anti-epileptic drugs, alter enzyme activity by causingmore or less of the enzyme to be produced.

2) Metabolic control

Enzyme inhibitors are also important in metabolic control.Manymetabolic pathways in the cell are inhibited bymetabolites that control enzyme activity through allostericregulation or substrate inhibition.
http://en.wikipedia.org/wiki/Anticonvulsanthttp://en.wikipedia.org/wiki/Metabolic_pathwayhttp://en.wikipedia.org/wiki/Metabolitehttp://en.wikipedia.org/wiki/Allosteric_regulationhttp://en.wikipedia.org/wiki/Allosteric_regulationhttp://en.wikipedia.org/wiki/Allosteric_regulationhttp://en.wikipedia.org/wiki/Allosteric_regulationhttp://en.wikipedia.org/wiki/Allosteric_regulationhttp://en.wikipedia.org/wiki/Metabolitehttp://en.wikipedia.org/wiki/Metabolic_pathwayhttp://en.wikipedia.org/wiki/Anticonvulsanthttp://en.wikipedia.org/wiki/Anticonvulsanthttp://en.wikipedia.org/wiki/Anticonvulsant


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inhibition -robin1 2003

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