(FEB 2022-1)
71. Following statements are made about uncompetitive inhibition of an enzyme:
A. Uncompetitive inhibitor binds to both free enzyme as well as an enzyme- substrate complex.
B. Addition of uncompetitive inhibitor lowers the Vmax of the reaction.
C. Apparent KM of the enzyme is lowered.
D. Apparent KM of the enzyme remains unchanged.
Which one of the following option represents the correct combination of the statements?
(1) B and C (2) A and C
(3) A and B (4) A and D
The correct answer is (1) B and C.
Introduction
Enzyme inhibition is a fundamental concept in understanding biochemical reaction regulation and pharmacology. Among inhibition types, uncompetitive inhibition stands out for its unique mechanism: the inhibitor binds exclusively to the enzyme-substrate complex (ES), affecting both binding affinity and catalytic throughput. Analyzing how uncompetitive inhibitors modify kinetic parameters Km and Vmax is critical for interpreting enzyme assays and inhibitor action. This article clarifies key points about uncompetitive inhibition and identifies the correct statements based on classic enzyme kinetics.
Key Characteristics of Uncompetitive Inhibition
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Binding site: Only to the ES complex, not free enzyme.
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Kinetic effects: Lowers both Vmax and the apparent Km.
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Mechanistic rationale:
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Binding of inhibitor stabilizes ES complex, reduces product formation rate (lower Vmax).
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Stabilization effectively increases substrate affinity (lower Km) since ES complex removal reduces free enzyme signal.
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Statement Analysis
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A. Incorrect
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Uncompetitive inhibitor does not bind free enzyme, only to ES complex.
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B. Correct
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Addition of uncompetitive inhibitor lowers Vmax by inactivating ES complexes.
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C. Correct
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Apparent Km is lowered due to inhibitor binding shifting equilibrium toward ES.
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D. Incorrect
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Km does not remain unchanged; it decreases in uncompetitive inhibition.
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Explanation of the Correct Combination
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The true statements are B and C.
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This combination reflects the core features of uncompetitive inhibition consistent with biochemical and kinetic studies.
Graphical Representation
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On Lineweaver-Burk plots, uncompetitive inhibition results in parallel lines, reflecting proportional decreases in Km and Vmax.
Biological Relevance
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Uncompetitive inhibition, though less common, plays important roles in metabolic regulation, especially in pathways where substrate accumulation needs tight control.
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It is crucial in the design of drugs targeting multi-substrate enzymes.
Summary Table
| Statement | Correctness | Explanation |
|---|---|---|
| A | False | Does not bind free enzyme, only ES |
| B | True | Lowers Vmax |
| C | True | Lowers apparent Km |
| D | False | Km does not remain unchanged |
Conclusion
For uncompetitive inhibition, the inhibitor binds only to the enzyme-substrate complex causing both Vmax and Km to decrease. Thus, the correct combination of statements from the given options is (1) B and C.
39 Comments
yashika
September 12, 2025Uncompetitive inhibitor binds only es complex and reduce both vmax and km
Khushi Vaishnav
September 12, 2025Apparent KM of the enzyme is lowered
and remain unchanged.
Kirti Agarwal
September 12, 2025In uncompetative inhibitors V max and km is decreased
Opt a
anjani sharma
September 12, 2025In uncompetative inhibition, v max and km both are decrease
Sakshi yadav
September 12, 2025A . addition of uncompetitive inhibitor lowers the Vmax of the reaction.
C. apparent KM of the enzyme is lowered.
Bharti yadav
September 12, 2025Addition of uncompetitive inhibitor lowers the Vmax of the reaction.
Apparent KM of the enzyme is lowered.
Varsha Tatla
September 13, 2025Does not bind with ree enz only bind with ES in un compitative inhibition
Km unchanged Vmax decrease
Kajal
September 13, 2025Option A is correct answer as km value decrease in uncompetitive binding n vmax also lowered by Alpha
Aakansha sharma Sharma
September 13, 2025In uncompetative inhibition, v max and km both are decrease
Kanica Sunwalka
September 13, 2025in uncompetitive inhibition : vmax decreases and apparent km also decreased by alpha
Rishita
September 13, 2025Decrease both vmax and km
Pratibha Jain
September 14, 2025correct answer is option (1) B and C.
Santosh Saini
September 14, 2025In uncompetitive inhibition the inhibitor binds only to the EScomplex bcz inhibitors loves EScomplex and prevent the catalysis of ES into E+S , and prevent the dissociation of EScomplex into E+S hence affinity increase , so km decrease and Vmax also decrease
Aartii sharma
September 14, 2025Option b&c
Konika Naval
September 14, 2025Vmax and Km ,both decreases in uncompetitive inhibition.
Dharmpal Swami
September 14, 2025Uncompetative inhibition= km and Vmax.both are decreased
Pallavi Ghangas
September 14, 2025In uncompetitive inhibition inhibitor bind to ES complex and increases the affinity of substrate for enzyme hence lower the km and all enzymes are in form of ES At infinite subtrate concentration where V Max is also lowered by Alpha
Ankita Pareek
September 14, 2025In an uncompitative inhibition inhibitor binds to ES complex so that both km and Vmax decrease
Palak Sharma
September 14, 2025Addition of uncompetitive inhibitor lowers the Vmax of the reaction as well as
the Km of the enzyme.
Priya dhakad
September 14, 2025In uncompetitive inhibition the inhibitor binds only ES complex causing vmax and km both are decreased.
Soniya Shekhawat
September 15, 2025The uncompetitive inhibitor binds only to the enzyme-substrate complex (ES), forming an inactive ESI complex so both km and vmax is Decrease.
Vanshika Sharma
September 15, 2025Both km and Vmax is decreses
Mohd juber Ali
September 15, 2025Statement B and C correct
Bcz in uncompetative inhibition affinity increase and the addition of inhibitor lower then v max
Lokesh Kumawat
September 15, 2025Uncompetitave inhibition inactive ESI complex so both km and vmax is Decrease.
Bhawna Choudhary
September 15, 2025In un compititive inhibition both km and vmax is decreased
Mahima Sharma
September 16, 2025Addition of uncompetitive inhibitor lowers the Vmax of the reaction.
And Apparent KM of the enzyme is lowered.
Sakshi Kanwar
September 16, 2025In uncompetitive inhibition enzyme lowers the Vmax and also lowers the Km
Aafreen Khan
September 16, 2025Option 1 – B and C is correct answer
Both Km and Vmax decreases in uncompetitive inhibition
Nilofar Khan
September 16, 2025Correct answer is B and C
B. Addition of uncompetitive inhibitor decreased the Vmax of the reaction.
C km value decrease
Payal Gaur
September 16, 2025B and C Vmax decrease and km decrease in uncompetitive inhibition
priti khandal
September 17, 2025in uncompetitive inhibition vmax and km both are decrease
Khushi Agarwal
September 17, 2025Option b and c is correct answer
Vmax and km both are decres
Tanvi Panwar
September 17, 2025In uncompetitive inhibition Km and Vmax. of the enzyme are lowered so 1 option is correct.
Priya khandal
September 17, 2025Decrease the km and v done sir b and c is right
Avni
September 17, 2025Addition of uncompetitive inhibitor lowers the Vmax of the reaction and KM of the enzyme is also lowered.
Asha Gurzzar
September 19, 2025Option 1 b and c is correct
Minal Sethi
September 19, 2025Option 1
by adding uncompetitive inhibitor vmax decreases and km also decreases
Muskan Yadav
September 19, 2025Option 1 – B and C is correct answer
Both Km and Vmax decreases in uncompetitive inhibition.
Kajal
September 25, 2025Option B and C is Correct:-
B- Addition of uncompetitive inhibitor lowers Vmax by inactivating ES complexes.
C- Apparently Km is lowered due to inhibitor binding shifting equilibrium toward ES.