Enzyme affinity inversely relates to Km (substrate concentration at half Vmax)

Steps:

• Determine Vmax for each enzyme from the graph's maximum rate.
• Locate [S] where rate equals Vmax/2 for X, Y, and Z.
• Compare [S] values: lowest [S] indicates lowest Km and highest affinity.
• Order affinities from lowest to highest Km: X (lowest Km), Z, then Y (highest Km).

Why B is correct:

• B (X > Z > Y) matches the Km order, as higher affinity means lower Km per Michaelis-Menten kinetics.

Why the others are wrong:

• A: Incorrectly places Y before Z, ignoring Z's lower Km than Y.
• C: Wrongly ranks Y highest affinity, but Y requires highest [S] for half Vmax.
• D: Misorders Z above X, but X has the lowest Km.

Final answer: B