Q.46 An enzymatic reaction is described by the following rate expression:
v =
vmS
km + S + S2 / ks
Which one of the following curves represents this expression?
Question Overview
An enzymatic reaction is described by the following rate equation:
v = VmS / (Km + S + S2/Ks)
The objective is to identify which graphical curve correctly represents this rate expression.
Understanding the Rate Equation
This rate equation does not follow simple MichaelisβMenten kinetics.
- At low substrate concentration (S):
The S2/Ks term is negligible, and the reaction velocity increases with S. - At high substrate concentration:
The S2/Ks term dominates, increasing the denominator and reducing the reaction velocity.
This behavior is characteristic of substrate inhibition.
Expected Shape of the Curve
- Velocity increases with increasing substrate concentration
- Reaches a maximum value
- Decreases at high substrate concentration due to inhibition
The resulting plot of velocity (v) versus substrate concentration (S) is bell-shaped.
Correct Answer
Option (B)
Option (B) shows an initial increase in reaction velocity followed by a decrease at higher substrate concentrations,
which is the defining feature of substrate inhibition kinetics.
Final Conclusion
The presence of the S2/Ks term in the denominator introduces substrate inhibition at high substrate concentrations,
producing a bell-shaped velocity versus substrate curve.
Correct Answer: Option (B)
