Enzyme reaction rate decreases as substrate is depleted

Steps:

• High initial substrate concentration allows maximum enzyme activity, yielding high initial rate.
• As reaction proceeds, substrate concentration falls, reducing enzyme-substrate complexes.
• Rate follows Michaelis-Menten kinetics: v = V_max [S] / (K_m + [S]), decreasing as [S] drops.
• Reaction completes when substrate is exhausted, rate reaches zero.

Why C is correct:

• C depicts a smooth, exponential decay from high initial rate to zero, matching Michaelis-Menten model for substrate-limited reactions.

Why the others are wrong:

• A shows linear decrease, ignoring nonlinear kinetics at varying [S].
• B shows constant rate, which occurs only with excess substrate, not here.
• D shows increasing rate, contradicting substrate depletion.

Final answer: C