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an enzyme produced in the mucosal lining of the stomach
that acts to degrade protein. Pepsin is one of three
principal protein-degrading, or proteolytic, enzymes in
the digestive system, the other two being chymotrypsin
and trypsin. The three enzymes were among the first to
be isolated in crystalline form. During the process of
digestion, these enzymes, each of which is particularly
effective in severing links between particular types of
amino acids, collaborate to break down dietary proteins
to their components, i.e., peptides and amino acids,
which can be readily absorbed by the intestinal lining.
In the laboratory studies pepsin is most efficient in
cleaving bonds involving the aromatic amino acids,
phenylalanine, tryptophan, and tyrosine. Pepsin is
synthesized in an inactive form by the stomach lining;
hydrochloric acid, also produced by the gastric mucosa,
is necessary to convert the inactive enzyme and to
maintain the optimum acidity (pH 1–3) for pepsin
function. Pepsin and other proteolytic enzymes are used
in the laboratory analysis of various proteins; pepsin
is also used in the preparation of cheese and other
protein-containing foods.
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