A 4-year-old child presents with recurrent episodes of vomiting, lethargy, and hypoglycemia triggered by fasting. Enzyme assay shows that adding the substrate at increasing concentrations does not increase the reaction rate beyond a plateau, and a Lineweaver-Burk plot reveals that adding a fixed amount of an inhibitor shifts the y-intercept upward while leaving the x-intercept unchanged. Which type of inhibition is demonstrated?
- A Non-competitive inhibition ✓
- B Competitive inhibition
- C Uncompetitive inhibition
- D Irreversible inhibition
Correct answer: A. Non-competitive inhibition
Explanation
In pure non-competitive inhibition the inhibitor binds at a site other than the active site, so Vmax falls but Km is unchanged. On a Lineweaver-Burk plot this raises the y-intercept (1/Vmax increases) while the x-intercept (-1/Km) stays the same — exactly the pattern described. Competitive inhibition instead leaves Vmax (y-intercept) unchanged while raising Km; uncompetitive inhibition lowers both Vmax and Km, giving parallel lines.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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