An enzyme inhibitor raises the Km (from 2 mM to 8 mM) without changing Vmax. Increasing substrate concentration overcomes the inhibition. This inhibitor is best characterised as:

• A Non-competitive inhibitor binding at an allosteric site
• B Uncompetitive inhibitor binding only to enzyme-substrate complex
• C Irreversible inhibitor forming a covalent bond with the catalytic residue
• D Competitive inhibitor binding to the active site reversibly ✓

Explanation

A competitive inhibitor structurally resembles the substrate and binds reversibly to the enzyme active site, directly competing with substrate for binding. Kinetically: Km is increased (in this case 4-fold, from 2 to 8 mM) because a higher substrate concentration is needed to displace the inhibitor and achieve half-maximal velocity. Vmax is unchanged because at saturating substrate concentrations, all active sites are occupied by substrate and inhibitor is entirely displaced. On a Lineweaver-Burk plot, competitive inhibition shows lines intersecting at the y-axis (same Vmax, changed x-intercept). Non-competitive inhibitors reduce Vmax without changing Km; uncompetitive inhibitors reduce both Km and Vmax; irreversible inhibitors permanently reduce enzyme activity without kinetic reversibility.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.