Enzyme inhibition and its types.

2. ENZYME INHIBITION
PRESENTED BY KEHKASHAN SABIR
M.PHIL CHEMISTRY
SARHAD UNIVERSITY PESHAWAR

3.  Introduction
 Types of Inhibitors
 Irreversible inhibitor
 Reversible inhibitor
 Competitive inhibitor
 Non competitive inhibitor
 Un competitive inhibitor
CONTENTS

4. INHIBITORS
 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 inhibitors.
 For example, poisons like cyanide and antibodies.

6. TYPES OF ENZYME
INHIBITION
• Irreversible inhibitors
• Reversible inhibitors

7. IRREVERSIBLE ENZYME
• Irreversible inhibitors occupy or destroy the active site of an
enzyme permanently.
• They form strong covalent bond with the active site.
• Sometimes they physically block the active site.

8. EXAMPLES
• Very small concentrate of chemical reagents such as heavy
metals ions , Mercury (Hg), Silver (Ag) and Arsenic (As) or
certain iodine containing compounds completely inhibit some
enzymes.

9. REVERSIBLE INHIBITORS
• They form weak linkage with the enzyme.
• There effect is completely or partially neutralized by increasing the concentration of
substrate.
• They are further divided into 3 types:
1. Competitive Inhibitor
2. Non Competitive Inhibitor
3. Uncompetitive Inhibitor

10. COMPETITIVE INHIBITORS
• A competitive inhibitor is any compound which closely resembles the
chemical structure and molecular geometry of the substrate.
• The inhibitor competes for the same active site as the substrate molecule.
• A competitive inhibitor is usually reversible if sufficient substrate molecules
are available to ultimately displace the inhibitor.

11. • Therefore, the amount of enzyme inhibition
depends upon the inhibitor concentration,
substrate concentration and the relative affinity
of the inhibitor and substrate for the active site

12. EXAMPLE
 Sulfonamides, or sulfa drugs, are structurally related to sulfanilamide, an
analog of p-aminobenzoic acid, or PABA.

14. NON-COMPETITIVE INHIBITORS
• A Non-competitive inhibitor is a substance that interact with the enzyme,
but usually not at the active site.
• 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.
• This inhibitor is usually reversible.

16. EXAMPLE
• An example of a use for a non-competitive inhibitor
is in the use of cyanide as a poison (prevents aerobic
respiration).
• Cyanide is a poison which prevents ATP production
via aerobic respiration, leading to eventual death.

17. UNCOMPETITVE INHIBITOR
• Uncompetitive inhibitors bind only to the enzyme-substrate
complex and not to the free enzyme.

18. EXAMPLES
• Drugs to treat causes of poisoning by methanol or ethylene
glycol act as uncompetitive inhibitors.