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B/B — Bio & Biochem

Enzyme Inhibition and Protein Structure

Question 1 Refers to This Passage

Researchers purified a soluble metabolic enzyme and measured its initial reaction velocity at several substrate concentrations. They repeated the experiment with a fixed concentration of compound X. Temperature, pH, and enzyme concentration were held constant. Without X, the measured Vmax was 120 μmol/min and the apparent Km was 2.0 mM. With X, Vmax remained 120 μmol/min, while apparent Km increased to 6.0 mM. At sufficiently high substrate concentrations, the two reaction rates converged. The team then studied the enzyme's structure. Residue 45 lies in the hydrophobic core, far from the active site. Replacing this residue with a charged amino acid destabilized the folded enzyme in aqueous solution. A nonpolar substitution preserved its stability. The researchers proposed that both active-site interactions and the hydrophobic effect contribute to normal enzyme function.

Question 1B/B — Bio & BiochemmediumPassage-Based

Which inhibition mechanism best explains the effect of compound X?

Question 2B/B — Bio & BiochemmediumDiscrete

Which amino acid side chain is most likely to carry a positive charge at physiological pH?

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