![The correct answer is (3) Non-competitive inhibitor. Title Interpreting Double Reciprocal Equations: Identifying Non-Competitive Inhibition in Enzyme Kinetics Meta Description Learn how to distinguish non-competitive inhibition using changes in Lineweaver-Burk plot equations. See why only Vmax changes—classic for non-competitive inhibitors—in detailed biochemical analysis. Slug noncompetitive-inhibition-lineweaver-burk-double-reciprocal-equation Introduction Enzyme kinetics is foundational for understanding metabolic regulation and drug mechanisms. Identifying different inhibition types is pivotal when analyzing altered Lineweaver-Burk plots or double reciprocal equations. Non-competitive inhibition is characterized by a change in the y-intercept (reflecting Vmax) while Km remains unchanged. This article shows how to recognize non-competitive inhibition from the mathematical forms and the biochemical impact it has on enzyme activity. Double Reciprocal Equations Overview Given: Without inhibitor (X): 1 v 0 = K m V m a x ( 1 [ S ] ) + 1 V m a x v 0 1 = V max K m ( [S] 1 )+ V max 1 With inhibitor (X): 1 V 0 = K m V m a x ( 1 [ S ] ) + 1 V m a x ( 1 + [ X ] K X ) V 0 1 = V max K m ( [S] 1 )+ V max 1 (1+ K X [X] ) Analysis: Identifying Inhibition Type In the presence of inhibitor, the slope K m V m a x V max K m (linked to Km) is unchanged. The y-intercept is increased by a factor ( 1 + [ X ] K X ) (1+ K X [X] ), decreasing apparent Vmax but leaving Km unaltered. This matches the action of a non-competitive inhibitor, which binds at a site distinct from the substrate binding site and reduces enzyme activity regardless of substrate concentration. In competitive inhibition, the slope (dependent on Km) would increase; in uncompetitive inhibition, both Km and Vmax are affected proportionally. Mechanistic Understanding Non-competitive inhibitors bind to either free enzyme or the ES complex at an allosteric site. This reduces the overall number of catalytically competent enzyme molecules, decreasing Vmax. Importantly, Km (substrate affinity) remains unchanged—substrate can bind just as well, but some enzyme can’t convert it to product. Summary Table Inhibitor Type Double Reciprocal Equation Change Km Vmax Effect on Plot/Activity Competitive Slope increases, y-intercept unchanged ↑ — Can be overcome by substrate Non-competitive y-intercept increases, slope unchanged — ↓ Can’t be overcome by substrate Uncompetitive Both slope and y-intercept change ↓ ↓ Lower Km and Vmax Visual Summary Non-competitive inhibition: Lines (with and without inhibitor) have the same x-intercept (Km unchanged) but different y-intercepts (Vmax decreased). Conclusion The molecule X is a non-competitive inhibitor, as indicated by the unchanged Km and decreased Vmax represented in the altered double reciprocal equation. This is a classic kinetic pattern, crucial for enzyme pharmacology and molecular biology.](https://www.letstalkacademy.com/wp-content/uploads/2025/09/73.jpg)
The correct answer is (3) Non-competitive inhibitor.
Introduction
Enzyme kinetics is foundational for understanding metabolic regulation and drug mechanisms. Identifying different inhibition types is pivotal when analyzing altered Lineweaver-Burk plots or double reciprocal equations. Non-competitive inhibition is characterized by a change in the y-intercept (reflecting Vmax) while Km remains unchanged. This article shows how to recognize non-competitive inhibition from the mathematical forms and the biochemical impact it has on enzyme activity.
Double Reciprocal Equations Overview
Given:
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Without inhibitor (X):
1v0=KmVmax(1[S])+1Vmax
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With inhibitor (X):
1V0=KmVmax(1[S])+1Vmax(1+[X]KX)
Analysis: Identifying Inhibition Type
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In the presence of inhibitor, the slope KmVmax (linked to Km) is unchanged.
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The y-intercept is increased by a factor (1+[X]KX), decreasing apparent Vmax but leaving Km unaltered.
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This matches the action of a non-competitive inhibitor, which binds at a site distinct from the substrate binding site and reduces enzyme activity regardless of substrate concentration.
-
In competitive inhibition, the slope (dependent on Km) would increase; in uncompetitive inhibition, both Km and Vmax are affected proportionally.
Mechanistic Understanding
-
Non-competitive inhibitors bind to either free enzyme or the ES complex at an allosteric site.
-
This reduces the overall number of catalytically competent enzyme molecules, decreasing Vmax.
-
Importantly, Km (substrate affinity) remains unchanged—substrate can bind just as well, but some enzyme can’t convert it to product.
Summary Table
| Inhibitor Type | Double Reciprocal Equation Change | Km | Vmax | Effect on Plot/Activity |
|---|---|---|---|---|
| Competitive | Slope increases, y-intercept unchanged | ↑ | — | Can be overcome by substrate |
| Non-competitive | y-intercept increases, slope unchanged | — | ↓ | Can’t be overcome by substrate |
| Uncompetitive | Both slope and y-intercept change | ↓ | ↓ | Lower Km and Vmax |
Visual Summary
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Non-competitive inhibition: Lines (with and without inhibitor) have the same x-intercept (Km unchanged) but different y-intercepts (Vmax decreased).
Conclusion
The molecule X is a non-competitive inhibitor, as indicated by the unchanged Km and decreased Vmax represented in the altered double reciprocal equation. This is a classic kinetic pattern, crucial for enzyme pharmacology and molecular biology.
35 Comments
yashika
September 12, 2025Non competitive inhibitor is unchanged km and reduced vmax in altered double reciprocal
Kirti Agarwal
September 12, 2025In non competative km is unchanged but v max is decrease
Kirti agarwal
September 29, 2025UnCompetitive inhibitors
Khushi Vaishnav
September 12, 2025Non-competitive inhibitor.
Sakshi yadav
September 12, 2025Non competative inhibitor km not change but vmax less
Varsha Tatla
September 13, 2025Non compitative inhibitors
For this inhibitors Vmax will decrease and km is un changed
Kajal
September 13, 2025This is non competitive inhibitor bcz here vmax decreases but the km remains the same so according to this option 3is correct
Asha Gurzzar
September 13, 2025Non competitive inhibitor as km remain same and vmax decrease
Kanica Sunwalka
September 13, 2025in case of Non competitive inhibitor – km : unchanged
vmax : reduced
Aakansha sharma Sharma
September 13, 2025This is non competitive inhibitor bcz here vmax decreases but the km remains the same so according to this option 3 is correct
Rishita
September 13, 2025non-competitive inhibitor, as indicated by the unchanged Km and decreased Vmax represented in the altered double reciprocal equation. This is a classic kinetic pattern, crucial for enzyme
Pratibha Jain
September 14, 2025correct answer is (3) Non-competitive inhibitor. bcz here vmax decreases but the km remains the same
Santosh Saini
September 14, 2025In non-competitive inhibition the km remain unchanged, while the Vmax decrease bcz inhibitors binds to an allosteric site means different site so reduce the enzyme activity
Aartii sharma
September 14, 2025Non competitive inhibitor
anjani sharma
September 14, 2025non-competitive inhibitor, as the unchanged Km and decreased Vmax is shown
Konika Naval
September 14, 2025Non competition inhibitor
Pallavi Ghangas
September 14, 2025Non competitive because Kmis unchanged where as Vmax is different
Dharmpal Swami
September 14, 2025Non competitive inhibition=km no change but Vmax.are decreased
Palak Sharma
September 14, 2025Non competitive because Kmis unchanged where as Vmax is reduced.
Vijay kumar Meena
September 14, 2025Non-competitive inhibitor ✔️
Ajay Sharma
September 14, 2025Non competative because km is constant and Vmax is decreasing
Priya dhakad
September 14, 2025Non competitive inhibitor becoz km is unchanged and vmax is decreased.
Soniya Shekhawat
September 15, 2025Non competitive inhibition
Lokesh Kumawat
September 15, 2025Non competitive inhibition
Ankita Pareek
September 15, 2025In a non competitive inhibition km.is unchanged but Vmax is decreased
Mohd juber Ali
September 15, 2025In non competative inhibition kdi =kdi’ (km not change )
But vmax decrease
Aafreen Khan
September 16, 2025Option 3rd – non competitive
Km is unchanged and Vmax is decreased
Nilofar Khan
September 16, 2025In noncompetitive inhibition Vmax decrease and km is unchanged
Payal Gaur
September 16, 2025Non competitive inhibition vmax decrease and km is unchanged
priya khandal
September 17, 2025non competitive inhibition vmax decrease and km is unchanged
Khushi Agarwal
September 17, 2025Agar slope same ho Km same.
Agar intercept ↑ ← Vmax 1.
So it’s answer is non competative inhibition
Savita Garwa
September 17, 2025correct answer is (3) Non-competitive inhibitor. bcz here vmax decreases but the km remains the same
Tanvi Panwar
September 17, 2025In non- competitive inhibition Vmax. decreases .
Avni
September 17, 2025The molecule X is a non-competitive inhibitor
Asha Gurzzar
September 19, 2025Non competitive inhibitor