The correct answer is (3) Column A-ii, Column B-ii.

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Introduction

Dixon plots are essential tools in enzyme kinetics, allowing researchers to analyze and visualize enzyme inhibition data accurately. The choice of axes is fundamental for true interpretation of inhibition constants and kinetic mechanisms. This article explains the selection of appropriate axes for Dixon plots and why plotting reciprocal velocity $(1/v)$ against inhibitor concentration $[I]$ yields meaningful insight into enzyme inhibition, particularly when determining the inhibition constant KiKi.

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Dixon Plot: Principle and Application

• The Dixon plot visualizes enzyme inhibition by plotting $1/v$ (reciprocal of initial velocity) on the y-axis and inhibitor concentration $[I]$ on the x-axis.

• Lines are generated for different substrate concentrations; their point of intersection reveals the KiKi, indicating the potency of the inhibitor.

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Analysis of Correct Axis Selection

Given the table:

• Standard Dixon plot requires plotting $1/v$ versus $[I]$.

• So, option (3): Column A-ii ($1/v$), Column B-ii ($[I]$) is correct.

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Why Other Combinations Do Not Work

• Option 1 (iv, i): Plots $[I]$ vs $1/v$ – incorrect orientation, not standard Dixon.

• Option 2 (i, ii): Plots $v$ vs $[I]$ – non-linear and less interpretable.

• Option 4 (iii, iv): Plots $1/[I]$ vs $v$ – irrelevant for inhibition kinetics analysis.

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Practical and Scientific Relevance

• Correct plotting is crucial for obtaining reliable kinetic parameters.

• Dixon plots help identify type of inhibition and calculate accurate KiKi.

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Summary Table

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Conclusion

To correctly construct a Dixon plot for enzyme inhibition kinetics, select $(1/v)$ (Column A-ii) and $[I]$ (Column B-ii) as axes. This choice ensures clear, reliable analysis for determining inhibition mechanisms and constants, essential for both academic and industrial biochemical research.