What would happen if you reduce the incubation time to 30 minutes for tube 5 (pepsin, BAPNA, pH 7.0 buffer)?

• A. Optical density would decrease, potentially zero
• B. Optical density would increase
• C. Optical density would remain the same
• D. Optical density would become negative

Answer: (A)

The main idea is that the amount of product formed in an enzyme reaction determines the optical density you measure. If you shorten the incubation, there’s less time for the enzyme to act, so less product is formed and the absorbance drops accordingly.

In tube five you have pepsin with BAPNA at pH 7.0. Pepsin works best in acidic conditions, so at neutral pH its activity is very limited. That means the reaction already proceeds slowly, and shortening the time to 30 minutes reduces product formation even more. Consequently, the optical density would fall, potentially to zero if almost no product is produced in that timeframe. It wouldn’t increase, and optical density can’t be negative, so those options aren’t plausible.