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Questions and Answers
Which characteristic distinguishes irreversible inhibitors from reversible inhibitors?
Which characteristic distinguishes irreversible inhibitors from reversible inhibitors?
- Irreversible inhibitors form a stable, covalent bond with the enzyme. (correct)
- Reversible inhibitors permanently alter the enzyme's structure.
- Reversible inhibitors only bind at the active site.
- Irreversible inhibitors can be easily removed by dialysis.
How does a competitive inhibitor affect the Michaelis-Menten kinetic parameters?
How does a competitive inhibitor affect the Michaelis-Menten kinetic parameters?
- Decreases $K_M$, increases $V_{max}$.
- Increases $K_M$, no change in $V_{max}$. (correct)
- No change in $K_M$, decreases $V_{max}$.
- Increases $K_M$, decreases $V_{max}$.
What is the defining characteristic of uncompetitive inhibition?
What is the defining characteristic of uncompetitive inhibition?
- The inhibitor binds to either the free enzyme or the enzyme-substrate complex.
- The inhibitor binds covalently to the enzyme.
- The inhibitor binds only to the free enzyme.
- The inhibitor binds only to the enzyme-substrate complex. (correct)
Which type of reversible inhibitor alters both the apparent $K_M$ and $V_{max}$?
Which type of reversible inhibitor alters both the apparent $K_M$ and $V_{max}$?
In a Lineweaver-Burk plot, which type of inhibition is characterized by lines that intersect on the y-axis?
In a Lineweaver-Burk plot, which type of inhibition is characterized by lines that intersect on the y-axis?
Which type of inhibition is suggested by Lineweaver-Burk plot lines that are parallel?
Which type of inhibition is suggested by Lineweaver-Burk plot lines that are parallel?
What does the inhibition constant ($K_i$) represent?
What does the inhibition constant ($K_i$) represent?
For a competitive inhibitor, how does the apparent Michaelis constant ($K_{M-app}$) change in relation to the inhibitor concentration ([I]) and the inhibition constant ($K_i$)?
For a competitive inhibitor, how does the apparent Michaelis constant ($K_{M-app}$) change in relation to the inhibitor concentration ([I]) and the inhibition constant ($K_i$)?
In the presence of a competitive inhibitor, what adjustment should be made to the substrate concentration to restore the original reaction velocity?
In the presence of a competitive inhibitor, what adjustment should be made to the substrate concentration to restore the original reaction velocity?
How does an uncompetitive inhibitor affect the slope of the Lineweaver-Burk plot?
How does an uncompetitive inhibitor affect the slope of the Lineweaver-Burk plot?
Which scenario describes the action of a mixed inhibitor?
Which scenario describes the action of a mixed inhibitor?
Noncompetitive inhibition is considered a special case of which type of inhibition?
Noncompetitive inhibition is considered a special case of which type of inhibition?
Which of the following is true regarding the effect of a mixed inhibitor on $V_{max}$?
Which of the following is true regarding the effect of a mixed inhibitor on $V_{max}$?
In enzyme kinetics, what does a smaller $K_i$ value indicate about an inhibitor?
In enzyme kinetics, what does a smaller $K_i$ value indicate about an inhibitor?
How can the nature of reversible enzyme inhibition be determined experimentally?
How can the nature of reversible enzyme inhibition be determined experimentally?
Flashcards
Enzyme Inhibitors
Enzyme Inhibitors
Substances that decrease the rate of enzyme-catalyzed reactions.
Reversible Inhibitors
Reversible Inhibitors
Inhibitors that bind to enzymes through non-covalent interactions.
Irreversible Inhibitors
Irreversible Inhibitors
Inhibitors that form stable, covalent bonds with enzymes.
Competitive Inhibitor
Competitive Inhibitor
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Uncompetitive Inhibitor
Uncompetitive Inhibitor
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Mixed Inhibitor
Mixed Inhibitor
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Inhibition Constant (Ki)
Inhibition Constant (Ki)
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Lineweaver-Burk Plot
Lineweaver-Burk Plot
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Ki (Dissociation Constant)
Ki (Dissociation Constant)
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Rate Constant (k)
Rate Constant (k)
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Enzyme
Enzyme
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Substrate
Substrate
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Vmax
Vmax
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Michaelis Constant (Km)
Michaelis Constant (Km)
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Initial Velocity (Vo)
Initial Velocity (Vo)
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Study Notes
- Enzyme inhibitors' functions and uses can be described.
- The contrast between reversible and irreversible inhibitors can be explained
- The effects of competitive, uncompetitive, and mixed inhibitors can be described.
- K₁ can be defined.
- Kinetic data can be analyzed to determine the type of inhibition.
- Lineweaver-Burk plots can illustrate the differences in reversible inhibitors.
Vocabulary
- rate constant (k)
- enzyme
- substrate
- inhibitor
- competitive inhibitor
- uncompetitive inhibitor
- mixed inhibitor
- initial velocity (vo)
- Vmax
- Michaelis constant (KM)
- Inhibtion constant (K₁)
- The kinetics of an enzyme, measured as a function of substrate concentration, occurs in the presence and absence of 2mM of a competitive inhibitor.
- Different types of reversible inhibitors affect kinetic constants differently.
- Equilibrium dissociation constant for an enzyme-inhibitor complex (K₁) mathematically affects different reversible inhibitors.
- Lineweaver-Burk plots can distinguish types of reversible inhibitors.
- The affinity of an enzyme for an inhibitor is described by K₁.
- K₁ is the dissociation constant for an enzyme-inhibitor complex: El ⇌ E + I
- K₁ = [E][I]/[EI]
Kinetics of Competitive Inhibitors
- Vmax does not change
- 1/V intercept is unchanged by presence of inhibitor
- KM-app increases
- 1/[S] intercept shifts, so reciprocal value increases in presence of inhibitor
- KM changes by an inhibition factor: α = (1 + [I]/K₁)
- KM-app = KM (1 + [I]/K₁)
- In the presence of a competitive inhibitor, the Michaelis-Menten equation becomes: V₀ = Vmax[S] / KM(1 + [I]/K₁) + [S]
Kinetics of Uncompetitive Inhibitors
- Inhibitors bind to ES only, not free enzyme, so the dissociation constant is different (K₁'): ESI ⇌ ES + I
- K₁' = [ES][I]/[ESI]
- Vmax decreases
- 1/V intercept increases as inhibitor binds ES complex
- KM-app decreases becuase Inhibitor decreases [ES] because ESI is unproductive, and it appears to need less S to reach ½ maximal velocity
- Both KM-app and Vmax decrease by the same factor, so the slope (KM/Vmax) is unchanged
- In the presence of an uncompetitive inhibitor, the Michaelis-Menten equation becomes: V₀ = Vmax[S] / KM/(1+[I]/K₁) + [S]/(1+[I]/K₁) = α’
Kinetics of Mixed Inhibitors
- An inhibitor can bind to both free enzyme or ES, so both Kl and Kl' have an impact on the kinetics.
- Vmax decreases, with the 1/V intercept increasing in value.
- KM-app may increase, decrease, or not change, which depends on relative affinities of inhibitor for E (K₁) and ES (K₁').
- Noncompetitive inhibition is a special case of mixed inhibition when K₁ = K'.
- In the presence of a mixed inhibitor, the Michaelis-Menten equation becomes: V₀ = Vmax[S] / KM(1 + [I]/K₁) + [S](1 + [I]/Kı’)
Inhibitor Kinetics Summary
| Inhibition Type | Effect on KM | Effect on Vmax |
|---|---|---|
| Competitive | KM-app increases (x-intercept shifts to right) | None |
| Uncompetitive | KM-app decreases(x intercept shifts to left) | Decreases(y-intercept moves up) |
| Mixed | KM-app increases or decreasesKM may not change(noncompetitive inhibition) | Decreases(y-intercept moves up) |
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Description
Explore enzyme inhibition, covering functions, reversible vs. irreversible inhibitors, and the effects of competitive, uncompetitive, and mixed types. Define K₁ and learn to analyze kinetic data for inhibition types. Understand how Lineweaver-Burk plots illustrate differences in reversible inhibitors, aiding in enzyme kinetics analysis.
