Q.38 Determine the correctness or otherwise of the following Assertion (a) and the Reason (r).
Assertion: A very low amount of inhibitor can act as an activator for allosteric enzymes.
Reason: Allosteric enzymes follow Michaelis–Menten kinetics.
(A) both (a) and (r) are true and (r) is the correct reason for (a)
(B) both (a) and (r) are true but (r) is not the correct reason for (a)
(C) (a) is true but (r) is false
(D) (a) is false but (r) is true
Correct Answer: (C) (a) is true but (r) is false
A very low amount of inhibitor can act as an activator for allosteric enzymes through hormetic effects or partial agonism at specific concentrations, but allosteric enzymes fundamentally deviate from Michaelis-Menten kinetics, showing sigmoidal curves instead.
Option Analysis
-
(A): Incorrect. Reason (r) is false—allosteric enzymes exhibit cooperative binding with sigmoidal kinetics, not hyperbolic Michaelis-Menten curves.
-
(B): Incorrect. Reason (r) false; allosteric enzymes follow Monod-Wyman-Changeux (MWC) or Koshland-Némethy-Filmer (KNF) models.
-
(C): Correct. Low inhibitor concentrations can activate via biphasic dose-response (hormesis) or conformational selection, but (r) false as allosteric enzymes reject Michaelis-Menten kinetics.
-
(D): Incorrect. Assertion (a) true—trace inhibitors show activation windows before inhibition dominates.
Allosteric enzymes low amount inhibitor activation challenges Michaelis-Menten assumptions in Q.38 assertion-reason analysis. Biochemical engineering students must distinguish cooperative kinetics from hyperbolic models for accurate pathway regulation predictions.
Hormetic Inhibition-Activation
Trace inhibitors (10⁻⁹-10⁻⁷ M) bind allosteric sites inducing “R-state” favoring substrate access before T-state inhibition dominates. Aspartate transcarbamoylase (ATCase) shows CTP inhibition overcome by ATP activation, demonstrating concentration-dependent switching.
Kinetic Distinction
Michaelis-Menten assumes independent active sites (v = Vₘₐₓ[S]/(Kₘ+[S])); allosteric enzymes yield sigmoidal v vs [S] plots with Hill coefficients (n_H >1). Reason (r) false—cooperativity precludes simple MM kinetics.
GATE Biotechnology Context
Q.38 tests enzyme kinetics mastery critical for bioreactor optimization and metabolic engineering. Sigmoidal kinetics affect growth models (μ = μₘₐₓ Sⁿ/(K+Sⁿ)) versus Monod (n=1), directly impacting yield calculations in your microbial physiology work.
