An enzyme shows a linear Eadie-Hofstee plot (V vs V/[S]) that passes through the origin with a slope of -Km and y-intercept of Vmax. In the presence of a competitive inhibitor, which change is observed in the Eadie-Hofstee plot?

• A The y-intercept (Vmax) decreases; slope (−Km) unchanged
• B Both y-intercept and slope decrease proportionally
• C The plot becomes non-linear with a hook at high V/[S] values
• D The y-intercept (Vmax) is unchanged; the slope (−Km) becomes steeper (more negative) ✓

Explanation

In the Eadie-Hofstee plot (v versus v/[S]), the equation is: v = Vmax − Km(v/[S]). Competitive inhibition increases the apparent Km (Km,app = Km(1 + [I]/Ki)) while Vmax is unchanged (competitive inhibitor is overcome by excess substrate). In the Eadie-Hofstee plot, Vmax (y-intercept, at v/[S] = 0) remains the same, but the slope becomes more negative (steeper) because Km,app increases. This contrasts with a Lineweaver-Burk plot where competitive inhibition changes the x-intercept (−1/Km) but not the y-intercept (1/Vmax). Uncompetitive inhibition reduces both Vmax and Km; non-competitive reduces Vmax but leaves Km unchanged.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

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