Enzyme Inhibition

Question 1

Enzyme inhibition is…

Answer 1

Decreasing or stopping of enzyme activity

Question 2

Inhibitor:

Answer 2

Substance decreasing or inhibiting enzyme activity.

Question 3

He two types of inhibitors are classified according to… And they are…

Answer 3

Classified according to the similarity between the inhibitor and the substrate.
1) Competitive (similarity)
2) Non competitive (no similarity)

Question 4

How do therapeutic drugs work?

Answer 4

By the inhibition of a specific substrate.

Question 5

What is another name for competitive inhibition?

Answer 5

Enzyme substrate complex

Question 6

What are the 7 characteristics of competitive inhibition

Answer 6

1) inhibitor binds to active site (competes with substrate).
2) structural similarity.
3) Reversible.
4) Does not bind with (E.S) enzyme substrate complex.
5) Depends on substrate concentration.
6) E. I ( enzyme inhibitor) complex (inhibitor + enzyme).
7) Km increases (bus more substrate is needed to reach 1/2 vm), vm is not effected.

Question 7

Folic Acid Synthesis…

Answer 7

-Competitive inhibition
- sulfonamide (antibiotic) inhibiting dyhydropteroate synthase ( DHPS) from acting upon Para aminobenzoic acid (PABA) which turns to folic acid.

Question 8

Prothrombin synthesis…

Answer 8

• Competitive Inhibition.
• Dicumerol (anticoagulant) inhibiting vitamin K epoxied reductase from acting upon vitamin k (coagulant) which turns into prothrombin.
  Heparin is another anticoagulant.

Question 9

Inhibition of Xanthine oxidase…

Answer 9

-Competitive inhibition.
- Allopurinol (AKA zyloric) inhibiting xanthine oxidase from working upon xanthine which turned into uric acid.
- For gout treatment.

Question 10

Inhibition of Alcohol Hydrogenase…

Answer 10

• Competitive Inhibition.
• Ethanol (converted to acetaldehyde) inhibits alcohol dehydrogenase from working upon methanol which turns to formaldehyde.
• Optic neuropathy and blindness.

Question 11

The 5 characteristics of noncompetitive inhibition

Answer 11

1) no structural similarity
2) binds to allosteric site
3) E.I (enzyme inhibitor) /or E.S (enzyme substrate) complex: inhibitor + enzyme/substrate
4) irreversible (does not depend on substrate concentration)
5) Km is not effected, Vm increases

Question 12

The three types of non competitive inhibition

Answer 12

1) sulphahydryl group
2) cofactor
3) specific ion activator

Question 13

Inhibition of sulphahydryl (-SH) group

Answer 13

• Non competitive inhibition
• -SH inhibited by reduction (-SH —> S) by heavy metals like mercury Hg++ and lead Pb++.
  Metals take the h away they are the oxidizing agents.

Question 14

Inhibition of cofactors types:

Answer 14

• Non competitive inhibition
  1) Coenzyme inhibition
  2) Prosthetic group inhibition
  3) inhibition of metal ion activator

Question 15

Coenzyme inhibition

Answer 15

• Non competitive (cofactor) inhibition
• inhibition of pyridoxal phosphate coenzyme (PLP) by cyanide hydrazine acting on
  1) Transamination
  2) Decarboxylation
  3) Deamination

Question 16

Prosthetic group inhibition

Answer 16

• non competitive inhibition, cofactor inhibition.
  Carbon Monoxide (CO) or cyanide inhibiting cytochrome oxidase prosthetic group of enzyme from acting upon iron in the heme.

Question 17

Inhibition of metal ion activator (chelation) 2 types…

Answer 17

• non competitive inhibition (cofactor)
  1) Chelation of Ca+, which activates thrombokinase enzyme, by oxilate prevents coagulation.
  thrombokinase enzyme turned inactive prothrombin to active thrombin which causes coagulation.
  2) chelation of Mg by fluoride stops glycolysis since Mg is crucial for enolase.