The Question is from neet-chemistry surface-chemistry catalysis, and it was created by the author A.RAMA NAGESWARARAO

Question

A reaction is catalyzed by two enzymes, E1 and E2, acting in sequence. E1 follows Michaelis-Menten kinetics, while E2 shows positive cooperativity.  If the substrate concentration is significantly increased, which of the following is MOST likely to be observed?

A.RAMA NAGESWARARAO · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Enzyme kinetics, Michaelis-Menten kinetics, cooperative binding
 **Related Topics**: Enzyme saturation, reaction rate, substrate concentration
 **Prerequisites**: Understanding of Michaelis-Menten equation and the concept of cooperativity.
## SOLUTION PATHWAY
**Given Information**:
  * Enzyme E1 follows Michaelis-Menten kinetics:  $v = \frac{V_{max}[S]}{K_m + [S]}$ where $v$ is the reaction rate, $V_{max}$ is the maximum reaction rate, $[S]$ is the substrate concentration, and $K_m$ is the Michaelis constant.
  * Enzyme E2 exhibits positive cooperativity:  The rate increases disproportionately with increasing substrate concentration.
  * Substrate concentration is significantly increased.
**Method & Steps**:
 1. Analyze E1's behavior at high substrate concentration:
  Reasoning: As $[S]$ becomes much larger than $K_m$, the Michaelis-Menten equation simplifies to $v ≈ V_{max}$.  E1 becomes saturated; its rate plateaus.
  Formula/Rule: Michaelis-Menten equation
 2. Analyze E2's behavior at high substrate concentration:
  Reasoning: Because E2 shows positive cooperativity, increasing the substrate concentration beyond a certain point will lead to a disproportionately larger increase in the reaction rate compared to a non-cooperative enzyme.
  Key Point: Positive cooperativity means that the binding of one substrate molecule increases the affinity for subsequent substrate molecules.
 3. Consider the sequential action of E1 and E2:
  Reasoning: Since E1's rate plateaus at high $[S]$, the overall reaction rate will ultimately be limited by E2.  However, the initial increase in substrate concentration will cause a significant increase in the rate due to E2's cooperative binding, making the effect of E2 more pronounced than that of E1 at high substrate concentration.
  Result: The overall reaction rate will increase, but the rate enhancement due to E2 will be more pronounced than that due to E1.
  Verification:  The saturation of E1 prevents a proportional increase in the overall reaction rate. The cooperative nature of E2 ensures a significant rate enhancement even after E1 saturates.
 ## OPTION ANALYSIS
A :x:  Incorrect. The rate will not increase proportionally because E1 will saturate.
B :x:  Incorrect. While E1 saturates, E2's positive cooperativity will still lead to a further increase in the overall rate.
C ✓: Correct. This option accurately reflects the combined effects of E1 saturation and E2's positive cooperativity.
D :x: Incorrect.  Substrate excess usually leads to saturation, not inhibition, in this context.  Inhibition would be more likely if there were a separate inhibitory site.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Ignoring the effect of E2's positive cooperativity:  Students might only focus on E1's saturation.
  2.Assuming a simple additive effect of the two enzymes:  The sequential and cooperative nature of the enzymes needs to be considered.
 **Quick Tips**:
  1.Remember the shape of the Michaelis-Menten curve and how it relates to saturation.
  2.Visualize the sigmoidal curve characteristic of enzymes exhibiting positive cooperativity.

A.RAMA NAGESWARARAO · Answer

The overall reaction rate will increase proportionally to the substrate concentration.

A.RAMA NAGESWARARAO · Answer

The reaction rate will plateau because E1 becomes saturated.

A.RAMA NAGESWARARAO · Answer

The correct Option is "The overall reaction rate will increase, but the rate enhancement due to E2 will be more pronounced than that due to E1."

A.RAMA NAGESWARARAO · Answer

The reaction will be inhibited due to substrate excess.

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