ALI RAZA

BS ZOLOGY 5th SEMESTER

ROLL #4029

Enzyme inhibition

¤ Introduction

¤ Types of Inhibitor

¤ Irreversible inhibitor

¤ Example

¤ Reversible inhibitor

¤ Competitive inhibitor

¤ Noncompetitive inhibitor

Contents

• A chemical substance which can react in place of substrate with the enzyme but is not transferred into products and block the active site of the enzyme temporarily or permanently is called inhibitor. For example, poisons like cyanide, antibodies anti-metabolites and some drugs.

Inhibitor

Types of inhibitor

• There are two type of inhibitor:

• Irreversible inhibitor

• Reversible inhibitor

Irreversible inhibitors

• Irreversible inhibitors occupy or destroy the active sites of the enzyme permanently and decrease the reaction rate. They form covalent bond with the active sites and occupy it. sometime they physically block the active sites.

Example of irreversible

• Very small concentrations of chemicalreagents such as the heavy metal ionsmercury(HG),silver(AG)and.arsenic (AS) or certain iodine-containingcompounds completely inhibit someenzymes.

Reversible inhibitors

• They form weak linkages with the enzymes. Their effect is completely or partly neutralized by increasing the concentration of the substrate. They are further divided into two major types:

• Competitive

• and non-competitive

Competitive inhibitor

• 1)A competitive inhibitor is any compound which

closely resembles the chemical structure and molecular geometry of the substrate. 2)The inhibitor competes for the same active site as the substrate molecule.

• 3) a competitive inhibition is usually reversible if sufficient substrate molecules are available to ultimately displace the inhibitor.

• 4) Therefore, the amount of enzyme inhibition depends upon the inhibitor concentration, substrate concentration, and the relative affinities of the inhibitor and substrate for the active site.

Non-competitive inhibitor• 1) A non-competitive inhibitor is a

substance that interacts with the enzyme, but usually not at the active site. 2) The non-competitive inhibitor reacts either remote from or very close to the activesite. 3) The net effect of a non competitive inhibitor is to change the shape of the enzyme and thus the active site, so that the substrate can no longer interact with the enzyme to give a reaction.

• 4) Non competitive inhibitors are usually reversible, but are not influenced by concentrations of the substrate as is the case for a reversible competive inhibitor.

•

Examples

1) Cyanide combines with the Iron in the enzymes cytochrome oxidase.

2) Heavy metals, Ag or Hg, combine with –SH groups.

• Heavy metals like lead, mercury (breaks disulfide bonds), chromium will act as non-competitive inhibitors