Consumed
proteins or polypeptides begin to be broken down in the stomach under the
action of the protease pepsin (4). Pepsin is secreted by chief cells in the
gastric mucosa as pepsinogen, a larger inactive form of the enzyme, also known
as a zymogene. Gastric acid (Hal, secreted by the parietal cells) alters the
conformation of pepsinogen so that it can cleave itself and become active
pepsin in the stomach. Gastric acid also denatures the proteins, which
partially unfolds them so that proteases have better access to their peptide
bonds. Pepsin (an end peptidase) in the stomach begins to hydrolyze proteins at
various cleavage points to smaller polypeptides (6). Pepsin has a higher
specificity for cleaving peptide bonds in which the carboxyl group is provided
by aromatic amino acids such as tyrosine, phenylalanine, tryptophan, and leonine
(6). Although pepsin can partially digest
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