Lecture 2: Enzyme Catalysis Inhibition Flashcards
How do principles of molecular recognition described for antibodies hold for any protein interaction, i.e. enzyme substrates, cofactors, small molecule ligands and
inhibitors?
Similar factors are involved for all ligands binding enzymes, including inhibitors and FDA approved drugs. Factors include complementary interactions, some degree of conformational change (induced fit) and substrate binding site is relatively small.
How are Km or Vmax or both affected by small molecule inhibitors?
Competitive inhibitor: only binds to free enzyme, changing Km value compared to uninhibited enzyme. Can bypass by flooding enzyme with substrate.
Noncompetitive inhibitor: binds free enzyme and enzyme/substrate complex, chaning Vmax compared to uninhibited enzyme.
Uncompetitive inhibitor: only binds to enzyme/substrate complex, decreasing Vmax and Km values compared to uninhibited enzyme.
What does Ki stand for? What is it analogous to?
Ki is the inhibitory equilibrium binding constant, (analogous to Kd) that defines the affinity of the inhibitor and is related to drug efficacy.
What are apparent values determined for Km and Vmax in the presence of an inhibitor compared to actual values?
The absence of inhibitors results in the actual values. The presence of inhibitors can result in an apparent change to Km or Vmax of both resulting in the new apparent value.
How can the change in Lineweaver-Burke plot distinguish the different types of inhibition and dependence on inhibition concentration?
Inhibitor always increases the line to the upper left.
Competitive: Km on the x axis increases while the Vmax remains the same. Slope changes and y intercept remains the same.
Noncompetitive: Km on the x axis remains the same and Vmax is reduced. Slope and y intercept change.
Uncompetitive: Km on the x axis is reduce and Vmax is reduced. Slope remains the same and the y intercept changes.
Concept: What is the value of Ki using a Lineweaver-Burke plot.
alpha = (1+ [i]/ Ki)
