Most enzymes act in pH between and
, a range that corresponds to the
general acidic level of cells and .
There are enzymes, however, that act
only under very acid or very basic pH.
So enzyme activity depends on pH
interval.

In the , for example, the gastric
juice has a very low pH, around 2, and
there the enzyme pepsin acts to
intensively digest proteins.

In the , pancreatic secretions
increase the pH of the enteric juice for
the action of other enzymes,
for example, trypsin.