Chapter 14- Enzyme Inhibition Flashcards
Inhibitors are substances that interfere with ______ by _______ enzymatic reactions
catalysis
slowing or halting
Two classes of inhibitors:
- Reversible
- Irreversible
Reversible inhibitors use _____ bonds that form ____ but break _____
weak
rapidly
easily
Which type of inhibitor does not permanently disable the enzyme?
reversible inhibitors
Reversible inhibitors come to an equilibrium with the enzyme to form ____
enzyme inhibitor complex (EI)
Irreversible inhibitors are known as:
enzyme inactivators
Irreversible inhibitors combine with enzymes through _____
strong (usually) covalent bond
An enzyme is ___ when paired with an irreversible inhibitor
permanently disabled
irreversible inhibitors are ______ dependent
time
for irreversible inhibitors, you cannot apply____
Michaelis-Menton kinetics
Depending on their nature, reversible inhibitors will effect____ or _____
Km
Vmax
Km and Vmax are measured in _______ which gives the ____
presence of inhibitor
apparent Km or Vmax
Competitive inhibitors _____ with substrate binding
compete
The substrate and competitive inhibitor are typically ____
mutually exclusive
Competitive inhibitors typically binds ____- to the enzyme
reversibly
The winner of the competition between competitive inhibitors and substrates depends on the ______
the concentration of each.
Competitive inhibitors bind to _____ but not to _____
free enzyme
ES complex
Competitive inhibitors will _____ Km, because ____
increase
because there is no affinity for S when EI has been made which reduces affinity and increases Km
Competitive inhibitors will ___ Vmax, because ____
not change
Vmax is the velocity of very high [S] which means inhibitor will not inhibit the enzyme bc it is out competed and doesn’t slow down the rxn
Uncompetitive inhibitor is ____ of binding to free E
incapable
Uncompetitive inhibitors only bind to the _____
ES complex
How do uncompetitive inhibitors inactivate the enzyme?
causes structural distortion of the active site
Effect of low [S] on uncompetitive inhibitors
inhibitor cannot bind bc most enzyme are free, making the inhibitor ineffective
Effect of high [S] on uncompetitive inhibitors
Inhibitor can bind bc most E is in ES complex, making the inhibitor effective.
Effect of high [Inhibitor] on competitive inhibitors
able to bind because [S] is out-competed which reduces [free Enzyme]
Effect of high [S] on competitive inhibitor
S out-competes inhibitor which makes it ineffective
Uncompetitive inhibitor effect on Km, why??
Decreases Km
effectively reduces [ES] which pulls the equilibrium towards [ES]. This increases the amount of S that binds to E which increases the affinity
uncompetitive inhibitor effect on Vmax. Why?
Decrease Vmax
inhibitor effective at high [S], effectively reduces [ES] and [E]. Vmax= K2[E]
Competitive inhibition effect on Lineweaver Burke plot:
- No incr in Km
- No change in Vmax
Uncompetitive inhibition effect on Lineweaver Burke plot:
Both Km and Vmax are decreased
leading to parallel lines
Noncompetitive inhibitors can bind to ___
either E or ES
Noncompetitive inhibitors will bind to _____
a site remote from the active site
Noncompetitive inhibitors prevent E from ___
turning substrate into product
With noncompetitive inhibitors, EI and ESI are ____
un reactive
Two classes of mixed inhibitors
- pure noncompetitive
- Mixed noncompetitive
Pure noncompetitive inhibitors
binding of I does not affect S binding (rare case)
Mixed noncompetitive inhibitors
binding of inhibitor reduces affinity of S for E (or ES)
How does pure noncompetitive inhibition affect Km and Vmax?
- Km is unchanged
- Vmax is decreased
Why do pure noncompetitive inhbitors decrease Vmax?
reduces [ES] and [E] which reduces the total amount of enzyme, slowing the reaction
How does mixed noncompetitive inhibitors affect Km?
when K1<K1’ then Km increases
when K1>K1’ then Km decreases
How do mixed noncompetitive inhibitors affect Vmax?
Vmax is decreased in both cases of K1 and K1’
