What is the inactive form of the digestion enzyme pepsin?

• A. Pepsin
• B. Amylase
• C. Pepsinogen
• D. Lipase

Answer: (C)

Proteins that digest proteins are usually made as inactive precursors to protect the tissue that makes them. Pepsin is one such enzyme in the stomach and is secreted as pepsinogen by the stomach’s chief cells. When pepsinogen enters the very acidic environment of the stomach, the low pH causes a small part of the molecule to be cleaved away, turning it into the active enzyme pepsin. Once active, pepsin can start breaking down proteins into smaller peptides, and it can even promote more activation of pepsinogen in a self-accelerating process. That’s why pepsinogen is the inactive form. The other options aren’t the precursor form of pepsin—they represent either different enzymes (amylase, lipase) or the active form itself (pepsin).