Final answer:
An optical density greater than zero indicates that BAPNA digestion has occurred, meaning that the enzyme pepsin is active and capable of protein digestion.
Step-by-step explanation:
An optical density greater than zero indicates that there has been a change in the amount of absorbance of light through a sample, which typically means that a substance has been altered or degraded. In the context of the question, where BAPNA (N-alpha-benzoyl-DL-arginine p-nitroanilide) is the substrate used for testing enzyme activity, an increase in optical density suggests that BAPNA digestion has occurred.
Given that BAPNA is a substrate for the proteolytic enzyme pepsin, if BAPNA digestion has taken place, it implies that this enzyme is active and therefore, capable of breaking down proteins. Pepsin is an enzyme in the stomach that digests proteins in the highly acidic environment and its activity is influenced by the pH levels as it requires an acidic environment to be activated. If the pH were to be significantly raised, the activity of pepsin would be diminished, impacting protein digestion.
In conclusion, the correct answer to the question is that an optical density greater than zero indicates that BAPNA digestion has occurred and pepsin is active.