Types Of Enzyme Inhibition

Types Of Enzyme Inhibition

Describe competitive and non- competitive inhibition of enzymes with their examples.
Answer.

Competitive Inhibiton

• When the active site of the enzyme is occupied by a substance other than the substrate of the enzyme, its activity is inhibited.
• This is known as competitive inhibition
• It is a reversible type of inhibition
• In competitive inhibition both ES and EI complexes are formed during the reaction
• The affinity of the substrate for the enzyme is progressively decreased with the increase in concentration of the inhibitor, thus lowering the rate of enzymatic reaction
• However, when the concentration of substrate is increased, the effect of inhibitor can be reversed, forcing it out of the EI complex

Clinical Importance Of Competitive Inhibitors

• Allopurinol
  • Enzyme – Xanthine oxidase
  • Substrate – Xanthine
  • Inhibitor – Allopurinol
  • Significance – Treatment of gout
• Amphetamine
  • Enzyme – Monoamine oxidase
  • Substrate – Epinephrine
  • Inhibitor – Amphetamine
  • Significance – To elevate catecholamine levels

Non Competitive Inhibition

• This occurs when substances not resembling geometry of the substrate do not exhibit mutual competition.
• The sites of attachment of the substrate and inhibitor are different
• The inhibitor binds with a site on the enzyme other than the active site.
• The inhibitor may combine with both free enzyme and ES complex.
• There are 2 types of non competitive inhibition –
  • Reversible
  • Irreversible
• Reversible non competitive inhibition
  • If the inhibitor can be removed from its site of binding without affecting the activity of the enzyme, it is called reversible non competitive inhibition.
  • Example – heavy metal ions (lead, silver, mercury) inhibit enzymes by binding with the cysteinyl sulfhydryl groups.
• Irreversible non competitive inhibition
  • If the inhibitor can be removed from the site of binding only with the loss of enzymatic activity, it is called irreversible non competitive inhibition
  • Example – iodoacetate inhibits the enzyme glyceraldehyde 3-phosphate dehydrogenase