Lineweaver–Burk Signature of Non-competitive Inhibition: Which change is characteristic?
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AThe entire line shifts to the right with both intercepts fixed.
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BThe y-intercept (1/Vmax) increases while the x-intercept (−1/Km) remains approximately unchanged.
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COnly the x-intercept changes while the y-intercept is constant.
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DAll of these are equally correct.
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EThe slope decreases because Vmax increases.
Answer
Correct Answer: The y-intercept (1/Vmax) increases while the x-intercept (−1/Km) remains approximately unchanged.
Explanation
Introduction:Interpreting Lineweaver–Burk plots is central to distinguishing inhibition modes. Non-competitive inhibition has a specific graphical fingerprint that reflects a reduction in catalytic capacity (Vmax).
Given Data / Assumptions:
- True non-competitive case (inhibitor binds E and ES equally well).
- Michaelis–Menten kinetics; plotting 1/v vs 1/[S].
Concept / Approach:
In the non-competitive limit, Vmax decreases; Km remains essentially unchanged. On a double-reciprocal plot, this means 1/Vmax (y-intercept) increases, x-intercept (−1/Km) is nearly constant, and slope = Km/Vmax increases accordingly. Lines for different inhibitor levels intersect on or near the x-axis.
Step-by-Step Solution:
1) Recognize parameter mapping: y-intercept = 1/Vmax; x-intercept = −1/Km.2) Non-competitive inhibition lowers Vmax ⇒ y-intercept rises.3) Km unaffected ⇒ x-intercept about constant.4) Slope increases since denominator Vmax is reduced.Verification / Alternative check:
Families of LB lines under non-competitive inhibition commonly intersect on the x-axis; kinetic fitting to v = (Vmax/(1+I/Ki)) * S / (Km + S) reproduces the same geometry.
Why Other Options Are Wrong:
A: No uniform lateral shift occurs. C: x-intercept alone does not change; y-intercept does. D: They are not equally correct; only one statement matches the canonical pattern. E: Vmax does not increase; slope does not decrease.
Common Pitfalls:
Confusing non-competitive with competitive (y-intercept constant in competitive) or uncompetitive (both intercepts shift).
Final Answer:
The y-intercept (1/Vmax) increases while the x-intercept (−1/Km) remains approximately unchanged.