Enzyme inhibitors

• What is an Enzyme inhibitors

  Molecules that interact with an enzyme and alter its structure to reduce its activity
• What enzyme graph is used to investigate inhibitor action

  Lineweaver-Burke
• Two main types of inhibitor action

  • Irreversible
  • Reversible
• Irreversible inhibition

  Inhibitor binds permanently to enzyme, usually mimicking substrate to bind to catalytic centre. Becomes covalently attached to catalytic group during catalysis
• Types of reversible inhibition

  • Competitive
  • Non-competitive
  • Mixed non-competitive
  • Uncompetitive
• Competitive inhibition

  Inhibitor competes directly with substrate for active site binding
• Non-competitive inhibition

  Inhibitor binds in an allosteric fashion at a site other than the active site to the enzyme or enzyme substrate complex. This changes the active site structure decreasing the efficiency of the enzyme.
• Mixed non-competitive inhibition

  
  

  Binds allosterically and decreases the ability of the enzymes to bind substrate and decreases catalytic ability.
• Uncompetitive inhibition

  Inhibitor binds only to the enzyme-substrate complex.

  The inhibitor binds proximal to the active site, 'freezing' the substrate in position so it cannot be converted to product.
• What is prostaglandin H2 synthase

  Cyclooxygenase (Cox)
• Describe aspirin inhibition of Cox

  Aspirin binds to the active site and competes with arachidonate.

  The serine residue group nucleophilically attacks the aspirin acetyl group.

  Serine is acetylated and the catalytic activity is lost.
• What is a low dose of aspirin used for

  To prevent thrombosis by inhibiting Cyclooxygenase 1 in blood platelets. This prevents prostaglandin mediated platelet aggregation.
• What is a normal dose of aspirin used for

  As an analgesic by inhibiting cyclooxygenase 1 and 2.
• How do irreversible inhibitors bind

  Covalently to catalytic residue
• What is the Km of a competitive inhibitor

  Lower than the substrate
• What is the molecular name for asparin

  Acetylsalicylic acid
• Where is salicylic acid found naturally

  In the white willow or meadowsweet plants
• What type of drug is acetylsalicylic acid

  Nonsteroidal anti-inflammatory drug [NSAID]
• How does aspirin work

  By inhibiting cyclooxygenase and blocking prostaglandin synthesis
• What is the role of prostaglandin

  It is involved in the inflammatory response
• What memberns of the NSAIDs bind irreversibly

  Aspirin
• Why does aspirin bind irreversibly

  The addition of the acetyl group
• How many isoforms are there of cycloococygenase

  2
• What does Cox 2 do

  Mediates the inflammatory response
• Which isoform of Cyclooxygenase is constitutively expressed

  Cox 1
• What is the similarity between Cox1 and Co2, which means that aspirin is non-selective

  They both have a Serine 530 residue in the active site
• Describee the synthesis pathway for prostaglandin H2

  Arachidonate is cyclised to form prostaglandin G2.

  Peroxidase reduces prostaglandin G2 to form prostaglandin H2.
• Which form of prostaglandin is inactive

  G2
• Which form of prostaglandin is active

  H2
• Describe the structure of cyclooxygenase

  It has a Serine residue in the active site at position 530.

  The hydrophobic channel of the active site aligns the substrate.

  There is a haem complex using Iron 3+.
• What is an analgesic

  A pain killer
• What are the side effects of aspirin use

  Can cause stomach ulcers. Because prostaglandins prevent acid secretion.
• What is 5-fluorouracil used as

  A chemotherapy drug that blocks DNA synthesis by inhibiting pyrimidine base production
• What is the precruser for the inhibitor of thymidylate synthase

  5-fluorouracil is converted to F-dUMP.
• What reaction does thymidylate synthase catalyse

  The conversion of deoxyuridine monophosphate (dUMP) into deoxythymidine monophosphate (dTMP) for DNA production.
• Describe how 5-fluorouracil inhibits DNA synthesis

  5-fluorouracil is converted to F-dUMP which binds to the active site using covalent bonds. This irreversibly modifies the active site.

  The result is that deoxyuridine monophosphate (dUMP) cannot be converted to deoxythymidine monophosphate (dTMP).
• What is the precurser of an drug inhibitor called

  A prodrug
• Why can machaelis-mentin kinetics not be used fro irreversible inhibition

  Because the inhibitor renders the enzyme inactive the concentration of active enzyme is not constant.
• How does an irreversible inhibitor affect Vmax

  Vmax will decrease as the inhibitor renders some of the enzyme inactive.
• How does irrversible inhibition change Km

  Km will remain the same as the enzyme has the same affinity for the substrate