Definition of "pepsin" [pep•sin]

• A digestive enzyme found in gastric juice that catalyzes the breakdown of protein to peptides. (noun)
• A substance containing pepsin, obtained from the stomachs of hogs and calves and used as a digestive aid. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Plus the acid in the stomach activates an enzyme called pepsin that further degrades proteins into smaller peptide units."
• "There it picks up one of the chemicals, known as pepsin, that breaks food down in the stomach; in response, Trichinella starts to flail."
• "This juice contains a ferment called pepsin and hydrochloric acid."