OBB Practice Questions - Olimpíada Brasileira De Biologia Exam

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In steady-state enzyme kinetics described by the Michaelis-Menten formulation, an experimenter evaluates the effect of adding a reversible inhibitor to an enzymatic reaction. Lineweaver-Burk double-reciprocal plot analysis reveals that the lines obtained in the presence and absence of the inhibitor intersect precisely at the positive y-axis (same 1/Vmax). What type of inhibition is occurring, and how are the kinetic parameters affected?

Non-competitive inhibition, where the inhibitor binds equally to the free enzyme and ES complex at an allosteric site, reducing Vmax while leaving the apparent Km completely unchanged across all substrate concentrations Uncompetitive inhibition, where the inhibitor binds exclusively to the enzyme-substrate (ES) complex, causing a parallel shift in the Lineweaver-Burk plot and a proportional decrease in both apparent Km and apparent Vmax Competitive inhibition, where the inhibitor competes with the substrate for the active site, increasing the apparent Km while leaving the maximum velocity (Vmax) unchanged Irreversible suicide inhibition, where a covalent adduct forms permanently at the catalytic triad, reducing active enzyme concentration without altering substrate affinity of the remaining uninhibited enzyme pool

Correct Answer:

Competitive inhibition, where the inhibitor competes with the substrate for the active site, increasing the apparent Km while leaving the maximum velocity (Vmax) unchanged

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