The correct answer is

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Introduction

Quantitative analysis of enzyme inhibition is essential for both basic biochemistry research and drug development. The Dixon plot is a classic graphical method used to examine inhibition kinetics and determine the inhibition constant (KiKi). This article explains the right variables to plot based on the Dixon method and how to interpret its results for different inhibitor types.

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Dixon Plot Explained

• Dixon plot is used for analyzing kinetic data of enzyme-catalyzed reactions in the presence of varying concentrations of an inhibitor.

• The classical axes are: 1ViVi1 (reciprocal of initial velocity) vs $[I]$ (inhibitor concentration).

• Multiple lines are drawn for varying substrate concentrations; their intersection provides KiKi.

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Rationale for 1ViVi1 vs $[I]$

• The Dixon plot’s reciprocal velocity on the y-axis and inhibitor concentration on the x-axis linearizes the relationship predicted by enzyme inhibition equations.

• It is standard for both competitive and non-competitive inhibition studies.

• The point where lines intersect gives direct information about inhibition type and strength.

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Why Other Axes Are Incorrect

• ViVi vs $[I]$: Does not linearize inhibition data for proper KiKi computation.

• 1ViVi1 vs 1[I][I]1: Not standard for Dixon analysis; does not provide kinetic parameters directly.

• ViVi vs 1ViVi1: Irrelevant comparison, not linked to inhibitor concentration.

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Use in Drug Discovery and Biochemistry

• Rapid, visual assessment of inhibitor potency.

• Essential for distinguishing between competitive, non-competitive, and uncompetitive mechanisms.

• Basis for many pharmacological assays.

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Summary Table

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Conclusion

Dixon’s plot requires 1ViVi1 vs $[I]$, making option (3) correct for enzyme inhibition kinetic analysis. This approach allows for precise determination of the inhibitor’s kinetic effects and constant, foundational for both basic and applied enzyme research.