Enzyme Inhibition Flashcards
Define inhibitor
Compounds which slow down or stop enzymatic reactions
How are inhibitors given?
Exogenously
How do irreversible inhibitors work?
Form covalent/extremely tight bonds with functional group at the active site of the enzyme
Aka suicide inhibitors
Give examples of irreversible inhibitors
Nerve gases
Penicillin
How does penicillin act?
Irreversible inhibitor that blocks enzyme glycopeptide transpeptidase
Penicillin prevents cross-linking of peptidoglycan strands = no bacterial cell wall
How can bacteria overcome penecillin?
By synthetizing more transpeptidase enzyme
What is the mechanism of action for competitive inhibition?
Reversible = competes with substrate for binding to active site
These inhibitors are structural analogs of the substrate
What is the mechanism of action for uncompetitive inhibition?
Uncompetitive inhibitors bind the ES complex = to form ESI complex
Substrate needs to be bound to change shape for inhibitor binding site to be exposed
What is the mechanism of action for non-competitive inhibition?
Aka mixed inhibition
Does not compete with substrate for binding site = can bind E or ES
What does a LB-plot look like for competitive inhibitor?
Same Vmax = y intercept
Changed Km = x intercept
What does a competitive inhibitor mean for the kinetics?
Changes the affinity of the enzyme for the substrate
But reaction can still attain maximal velocity but adding more substrate to outcompete inhibitor
What does a LB-plot look like for an uncompetitive inhibitor?
It affects both the Vmax and Km
The lines are parallel
What does a LB-plot look like for non-competitive inhibitor?
Changes both the Km and Vmax
BUT in special cases Km is unchanged = so same x-intercept
How to calculate the alpha?
Km = apparent Km x alpha
Alpha = 1 + [I] / K_I
How to calculate apparent Km and Vmax for uncomp inhibition?
Apparent Km = Km / alpha-prime
Apparent Vmax = Vmax / alpha-prime
Alpha-prime 1 + [I] / K’_I
