Which tube shows the highest lipase activity in the described setup?

• A. Tube 3 (lipase, deionized water, bile salts, pH 9.0 buffer)
• B. Tube 1 (lipase, deionized water, pH 7.0 buffer, bile salts)
• C. Tube 2 (lipase, deionized water, pH 7.0 buffer, bile salts)
• D. Tube 4 (deionized water, vegetable oil, bile salts, pH 7.0 buffer)

Answer: (A)

Lipase activity rises when the enzyme is in its optimal environment and the substrate is accessible. Bile salts emulsify the oil, increasing surface area for the enzyme to act on, while an alkaline pH around 9.0 helps keep the lipase in a highly active state. The tube that contains lipase, deionized water, bile salts, and a pH 9.0 buffer has both the emulsified substrate and the most favorable pH, so it enables the fastest fat hydrolysis and the highest lipase activity. The tube with oil but no lipase has no enzyme to catalyze the reaction, so no activity occurs. Tubes with lipase at neutral pH are less active than at alkaline pH, explaining their comparatively lower activity.