Lecture 19: Enzymes

Question 1

Irreversible inhibition

Answer 1

• Drug or poisons
• Bind covalently to enzymes or cofactors = abnormal protein and enzyme is degraded –> inhibition can only be overcome by new enzyme without contact to drug

Question 2

DFP (Di-isopropyl fluorophosphate)

Answer 2

• Irreversible inhibitior of acetylcholinesterase
• DFP blocks rxn = acetylcholine accumulating =

1) CONTINUOUS MUSCLE CONTRACTIONS,
2) OVERSTIMULATION OF AUTONOMIC NERVOUS SYSTEM
3) BLURRED VISION
4) BRONCHOCONSTRICTION
5) SEIZURES
6) RESPIRATORY ARREST

Question 3

Aspirin

Answer 3

• Irreversible Inhibitor of cyclooxygenase (COX)
• Inhibits COX-1 and COX-2 = decrease in PROSTAGLANDINS AND THROMBOXANE synthesis
• Low dose = Reduced blood clot

Question 4

What are the functions of thromboxane and prostacyclin

Answer 4

Thromboxane
-Stimulates blood clotting

Prostacyclin:
-Reduces blood clotting

Question 5

Process of blood clotting

Answer 5

• COX needed
• Platelets release thromboxane
• Endothelial cells for release prostacyclin
• Aspirin inhibits COX
• Endothelial cells: Degrade enzyme and synthesize new cox that is active
• Platelets: Not able to be synthesizes new COX = less thromboxane (which is released from platelet)

Question 6

How is aspirin related to blood clotting?

Answer 6

• A low does of aspirin, changes the normal blood ratio of thromboxane and prostacyclins
• Low dose= less thromboxane = reduced blood clotting

Thromboxane < Prostacyclins (normal amount)

Question 7

Suicide inhibitor drugs

Answer 7

Enzyme itself changes the structure of the drug = irreversible inhibition

Question 8

Alluropurinol

Answer 8

• Used to inhibit xanthine oxidase during GOUT treatment to reduce uric acid formation
• Alloxanthine (oxypurinol) created when enzyme alters allopurinol
• Alloxanthine binds to molybdenum-sulfide complez in the active site which is needed for catalysis