The Collaborative International Dictionary of English v.0.48:

Pepsinogen \Pep*sin"o*gen\, n. [Pepsin + -gen.] (Physiol. Chem.)
   A proenzyme, the antecedent of the enzyme pepsin. A substance
   contained in the form of granules in the peptic cells of the
   gastric glands. It is readily convertible into pepsin. Also
   called propepsin.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Propepsin \Pro*pep"sin\, n. [Pref. pro- + pepsin.] (Physiol.
   Chem.)
   See Persinogen.
   [1913 Webster]