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Questions and Answers
In the context of enzyme kinetics, what does the proportionality (P [ES]) imply about the reaction?
In the context of enzyme kinetics, what does the proportionality (P [ES]) imply about the reaction?
- The reverse reaction from E + P to ES is favored.
- The enzyme is saturated with the substrate.
- The formation of the ES complex is the rate-limiting step.
- The breakdown of ES to E + P is the rate-limiting step. (correct)
According to the competitive inhibition model presented, (k_{-2}) is assumed to be zero, meaning the reaction (E + P EP ES) proceeds significantly in the reverse direction.
According to the competitive inhibition model presented, (k_{-2}) is assumed to be zero, meaning the reaction (E + P EP ES) proceeds significantly in the reverse direction.
False (B)
In a scenario where (P [ES]), the breakdown of ES to E + P is the __________ __________ __________ (RLS) of the reaction.
In a scenario where (P [ES]), the breakdown of ES to E + P is the __________ __________ __________ (RLS) of the reaction.
rate limiting step
Match the following descriptions with the correct components or assumptions from the competitive inhibition model:
Match the following descriptions with the correct components or assumptions from the competitive inhibition model:
Competitive inhibitors primarily affect enzymatic reactions by:
Competitive inhibitors primarily affect enzymatic reactions by:
In competitive inhibition, the inhibitor permanently alters the enzyme's active site, preventing any future substrate binding.
In competitive inhibition, the inhibitor permanently alters the enzyme's active site, preventing any future substrate binding.
In the context of enzyme kinetics, what is the primary consequence of a competitive inhibitor binding to an enzyme?
In the context of enzyme kinetics, what is the primary consequence of a competitive inhibitor binding to an enzyme?
A competitive inhibitor is most effective when its structure closely ______ the substrate.
A competitive inhibitor is most effective when its structure closely ______ the substrate.
Which of the following equations correctly represents the equilibrium constant (Ki) for the binding of an inhibitor (I) to an enzyme (E) to form an enzyme-inhibitor complex (EI)?
Which of the following equations correctly represents the equilibrium constant (Ki) for the binding of an inhibitor (I) to an enzyme (E) to form an enzyme-inhibitor complex (EI)?
In enzyme assays involving inhibitors, what is directly observed at the initial velocity stage?
In enzyme assays involving inhibitors, what is directly observed at the initial velocity stage?
According to the steady-state assumption, the rate of formation of the enzyme-substrate (E-S) complex is always greater than its rate of breakdown.
According to the steady-state assumption, the rate of formation of the enzyme-substrate (E-S) complex is always greater than its rate of breakdown.
Match the terms related to enzyme inhibition with their descriptions:
Match the terms related to enzyme inhibition with their descriptions:
In uncompetitive inhibition, to which form of the enzyme does the inhibitor bind?
In uncompetitive inhibition, to which form of the enzyme does the inhibitor bind?
Inhibitor I directly binds with the free form of the enzyme E in uncompetitive inhibition.
Inhibitor I directly binds with the free form of the enzyme E in uncompetitive inhibition.
What is the ratio in which the enzyme (E) and the substrate (S) bind to each other?
What is the ratio in which the enzyme (E) and the substrate (S) bind to each other?
In kinetic studies, what is varied at several inhibitor concentrations ([I0])?
In kinetic studies, what is varied at several inhibitor concentrations ([I0])?
The binding of the inhibitor to the enzyme always prevents substrate binding.
The binding of the inhibitor to the enzyme always prevents substrate binding.
In uncompetitive inhibition, what is the relationship between the inhibitor and the substrate?
In uncompetitive inhibition, what is the relationship between the inhibitor and the substrate?
In uncompetitive inhibition, increasing the substrate concentration can overcome the inhibition.
In uncompetitive inhibition, increasing the substrate concentration can overcome the inhibition.
In uncompetitive inhibition, both $K_M$, and _____ are altered.
In uncompetitive inhibition, both $K_M$, and _____ are altered.
What does the term 'dead-end complex' refer to in the context of uncompetitive inhibition?
What does the term 'dead-end complex' refer to in the context of uncompetitive inhibition?
The equilibrium constant, $K_i$, for uncompetitive inhibition represents the affinity of the inhibitor for the free enzyme.
The equilibrium constant, $K_i$, for uncompetitive inhibition represents the affinity of the inhibitor for the free enzyme.
Which of the following is true regarding the binding of the inhibitor in uncompetitive inhibition?
Which of the following is true regarding the binding of the inhibitor in uncompetitive inhibition?
Match the terms with their descriptions related to uncompetitive inhibition:
Match the terms with their descriptions related to uncompetitive inhibition:
In the context of enzyme kinetics, what does the slope of the double reciprocal plot represent when an inhibitor is present?
In the context of enzyme kinetics, what does the slope of the double reciprocal plot represent when an inhibitor is present?
The double reciprocal plot (Lineweaver-Burk plot) directly yields $V_{max}$ as the y-intercept.
The double reciprocal plot (Lineweaver-Burk plot) directly yields $V_{max}$ as the y-intercept.
Write the formula of the slope of a double reciprocal plot in the presence of an inhibitor, where $K_M'$ is the modified Michaelis constant, and $V_{max}$ the maximum rate.
Write the formula of the slope of a double reciprocal plot in the presence of an inhibitor, where $K_M'$ is the modified Michaelis constant, and $V_{max}$ the maximum rate.
In the equation for the double reciprocal plot in the presence of an inhibitor, the term that includes the inhibitor concentration [I] is $1 + \frac{[I]}{K_i}$, which modifies the ______.
In the equation for the double reciprocal plot in the presence of an inhibitor, the term that includes the inhibitor concentration [I] is $1 + \frac{[I]}{K_i}$, which modifies the ______.
Match the terms in enzyme kinetics with their representation in the double reciprocal plot:
Match the terms in enzyme kinetics with their representation in the double reciprocal plot:
How does the presence of a competitive inhibitor affect the slope of the double-reciprocal plot?
How does the presence of a competitive inhibitor affect the slope of the double-reciprocal plot?
According to the double reciprocal equation given, the x-intercept of the plot is influenced by the concentration of the inhibitor [I].
According to the double reciprocal equation given, the x-intercept of the plot is influenced by the concentration of the inhibitor [I].
According to the competitive inhibition model, what is the impact on $V_{max}$ and $K_M$?
According to the competitive inhibition model, what is the impact on $V_{max}$ and $K_M$?
In the equation slope = $\frac{K_M'}{V_{max}} = \frac{K_M}{V_{max}}(1 + \frac{[I]}{K_i})$, as [I] (the inhibitor concentration) increases, the value of $K_M'$ ______.
In the equation slope = $\frac{K_M'}{V_{max}} = \frac{K_M}{V_{max}}(1 + \frac{[I]}{K_i})$, as [I] (the inhibitor concentration) increases, the value of $K_M'$ ______.
In the derivation of enzyme kinetics with the assumption $k_{-2} = 0$, it is assumed that the product (P) does not readily convert back to the enzyme-substrate (ES) complex.
In the derivation of enzyme kinetics with the assumption $k_{-2} = 0$, it is assumed that the product (P) does not readily convert back to the enzyme-substrate (ES) complex.
Which of the following statements correctly describes the impact of a competitive inhibitor on the double reciprocal plot?
Which of the following statements correctly describes the impact of a competitive inhibitor on the double reciprocal plot?
In competitive inhibition, the apparent $K_M$, denoted as $K_M'$, is equal to $K_M (1 + [I]/ ____ )$ .
In competitive inhibition, the apparent $K_M$, denoted as $K_M'$, is equal to $K_M (1 + [I]/ ____ )$ .
In the equation $V_0 = \frac{V_{max} [S]}{[S] + K_M'}$, what does $K_M'$ represent in the context of competitive inhibition?
In the equation $V_0 = \frac{V_{max} [S]}{[S] + K_M'}$, what does $K_M'$ represent in the context of competitive inhibition?
Which equation correctly describes the relationship between total enzyme concentration $[E]_0$, free enzyme concentration $[E]$, enzyme-inhibitor complex $[EI]$, and enzyme-substrate complex $[ES]$?
Which equation correctly describes the relationship between total enzyme concentration $[E]_0$, free enzyme concentration $[E]$, enzyme-inhibitor complex $[EI]$, and enzyme-substrate complex $[ES]$?
The term $k_{-1}$ represents the rate constant for the formation of the ES complex from E and S.
The term $k_{-1}$ represents the rate constant for the formation of the ES complex from E and S.
Which of the following scenarios would result in an increase in the concentration of the enzyme-substrate complex [ES]?
Which of the following scenarios would result in an increase in the concentration of the enzyme-substrate complex [ES]?
What is the effect of a competitive inhibitor on a Lineweaver-Burk plot?
What is the effect of a competitive inhibitor on a Lineweaver-Burk plot?
Flashcards
Competitive Inhibition
Competitive Inhibition
A type of reversible enzyme inhibition where the inhibitor binds to the same active site as the substrate, preventing substrate binding.
Structural Similarity
Structural Similarity
The inhibitor often has a similar structure to the substrate.
Dead-End Complex
Dead-End Complex
The inhibitor binds to the enzyme, forming a complex that cannot proceed to form product. The substrate is blocked.
Inhibition Constant (Ki)
Inhibition Constant (Ki)
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Initial Concentrations
Initial Concentrations
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Steady-State Assumption
Steady-State Assumption
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Inhibitor Binding Target
Inhibitor Binding Target
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Reversible Inhibition
Reversible Inhibition
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P ∝ [ES] Meaning
P ∝ [ES] Meaning
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Why is k-2 = 0?
Why is k-2 = 0?
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V0 = k2 [ES] Meaning
V0 = k2 [ES] Meaning
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[S]0 and [I]0 >> [E]0
[S]0 and [I]0 >> [E]0
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Constant [S] and [I]
Constant [S] and [I]
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ES Complex Formation
ES Complex Formation
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Product Generation
Product Generation
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Inhibitor Binding in uncompetitive Inhibition
Inhibitor Binding in uncompetitive Inhibition
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Step 1: E + S
Step 1: E + S
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Step 2: ES + I
Step 2: ES + I
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Step 3: No Product
Step 3: No Product
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Effect on Kinetic Parameters
Effect on Kinetic Parameters
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ESI Complex
ESI Complex
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Overcoming Inhibition
Overcoming Inhibition
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KM and Vmax in Uncompetitive Inhibition
KM and Vmax in Uncompetitive Inhibition
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Inhibition Constant (Ki) for Uncompetitive Inhibition
Inhibition Constant (Ki) for Uncompetitive Inhibition
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Binding Order in Uncompetitive Inhibition
Binding Order in Uncompetitive Inhibition
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Dead-End Complex (ESI)
Dead-End Complex (ESI)
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Conformational Change
Conformational Change
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k−2 = 0 Assumption
k−2 = 0 Assumption
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Michaelis Constant (KM)
Michaelis Constant (KM)
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Enzyme Conservation
Enzyme Conservation
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Maximum Velocity (Vmax)
Maximum Velocity (Vmax)
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Initial Velocity (V0)
Initial Velocity (V0)
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Michaelis-Menten equation (V0)
Michaelis-Menten equation (V0)
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KM meaning
KM meaning
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Vmax definition
Vmax definition
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Competitive Inhibition Effects
Competitive Inhibition Effects
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Double Reciprocal Plot
Double Reciprocal Plot
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Lineweaver-Burk Plot Usage
Lineweaver-Burk Plot Usage
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Plot purpose.
Plot purpose.
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Slope of the Double Reciprocal Plot (Competitive Inhibition)
Slope of the Double Reciprocal Plot (Competitive Inhibition)
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Vmax
Vmax
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Apparent Michaelis Constant (KM')
Apparent Michaelis Constant (KM')
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[I]
[I]
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[S0]
[S0]
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Michaelis-Menten Equation
Michaelis-Menten Equation
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Study Notes
- Lecture #11 is on Enzyme Inhibition - Part 2
Reversible Inhibition
- Includes: competitive and uncompetitive inhibitions
Competitive Inhibition
- Competitive inhibitors often resemble the substrates whose reactions they inhibit.
- Structural similarity allows them to compete for the same binding site on the enzyme.
- The enzyme-bound inhibitor either lacks the appropriate reactive group or is held in an unsuitable position in the enzyme.
- This forms a dead-end complex.
- The inhibitor must dissociate from the enzyme and be replaced by substrate.
Competitive Inhibition Model
- Enzyme E and substrate S bind in a 1:1 ratio, forming a complex ES.
- Enzyme E acts on the substrates to generate product P, regenerating the enzyme
Competitive Inhibition Assumptions
- The E-S complex is in a steady-state, meaning the rate of complex formation from E and S is equal to the rate of its consumption.
- The breakdown of ES to E + P is the rate-limiting step (RLS) of the reaction, thus the reverse reaction can be ignored.
- The concentrations of [S] and [I] are much larger than [E]₀.
- Changes in [S] and [I] due to formation of ES and EI complexes are negligible.
Competitive Inhibition Derivation
- The conservation of mass dictates that [E]₀ = [E] + [EI] + [ES].
- Solving for [E], use the equilibrium constant for EI formation and the steady-state assumption for ES.
- No change in maximum velocity; apparent increase in Michaelis constant (KM)
Competitive Inhibition: Lineweaver-Burk Analysis
- Kinetic studies with varying substrate concentrations, [S₀], at several inhibitor concentrations, [I₀], help determine inhibition type and Ki.
- If inhibitor binding blocks the inhibitor-binding site through conformational change or other mechanisms, an identical expression and Lineweaver-Burk signature is obtained.
- Competitive inhibition plays a role in metabolic processes.
Uncompetitive Inhibition
- Uncompetitive inhibitors bind only to the ES complex, not the free enzyme.
- Substrate binding induces a conformational change in the enzyme, revealing an inhibitor binding site, or the inhibitor directly binds the enzyme-bound substrate.
- The inhibitor does not compete with the substrate for the same binding site.
- Increasing substrate concentration cannot overcome the inhibition.
- A dead-end complex ESI is formed.
- Both KM and Vmax are altered.
- The effect results in a distinctive kinetic pattern under steady-state conditions.
Uncompetitive Inhibition Model
- Our enzyme E mixed with a substrate S, they proceed to bind to each other in 1:1 ratio and form a complex ES.
- The enzyme E acts upon the substrates, generates product P and the enzyme is regenerated. ES complex may bind inhibitor I to yield the ESI complex.
Uncompetitive Inhibition Rare
- Uncompetitive inhibition patterns are seen with two-substrate reactions and this may help in the elucidation of the reaction mechanism.
- This is rare for single-substrate enzyme-catalysed reactions.
- Examples include: 1) inhibition of aryl sulphatase by hydrazine, and 2) inhibition of intestinal alkaline phosphatase by phenylalanine.
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