Slowed lipase reaction rate due to saturation and inhibition

Steps:

• The graph shows pH decreasing over time from lipid hydrolysis by lipase, producing acidic fatty acids; between 50-60 minutes, the rate of pH change slows or plateaus.
• Evaluate statement 1: Substrate limitation occurs if lipids are depleted, but high lipid proportion suggests this is unlikely early on.
• Evaluate statements 2, 4, and 5: Enzyme saturation (all active sites occupied) maintains Vmax initially; product inhibition by fatty acids reduces rate; statement 5 (likely equilibrium or similar) explains final leveling off.
• Eliminate 3: Denaturation by inhibitors is improbable, as inhibitors typically bind reversibly without permanent damage.

Why D is correct:

• D selects 2, 4, and 5, aligning with enzyme kinetics where saturation gives constant rate, then products inhibit, leading to plateau (Michaelis-Menten model).

Why the others are wrong:

• A includes 1 (substrate not limiting) and 3 (no denaturation evidence).
• B includes 1 (substrate not limiting) but misses 2 (saturation key).
• C omits 5 (needed for full plateau explanation).

Final answer: D