Product inhibition limits enzyme activity at higher concentrations

Steps:

• Identify glucose phosphate as the product of phosphorylase, which acts as an allosteric inhibitor.
• Interpret iodine test: color disappearance measures glycogen breakdown rate; faster at low glucose phosphate.
• Observe trend: at ≤25 mg dm⁻³ glucose phosphate, rapid decolorization indicates maximum rate.
• Conclude: low inhibitor allows full enzyme activity, so enzyme concentration limits the rate.

Why C is correct:

• In enzyme kinetics, without significant inhibition (at low product concentrations), the reaction rate reaches Vmax, limited by enzyme concentration per Michaelis-Menten model.

Why the others are wrong:

• A: Maximum rate produces glucose phosphate, not converts to it; irrelevant to trend.
• B: Glucose phosphate is inhibitory product, not substrate; substrate (glycogen) is constant.
• D: Reaction is phosphorolysis, not hydrolysis; phrasing unrelated to observed trend.

Final answer: C