The Collaborative International Dictionary of English v.0.48:

Trypsinogen \Tryp*sin"o*gen\, n. [Trypsin + -gen.] (Physiol.)
   The antecedent of trypsin, a substance which is contained in
   the cells of the pancreas and gives rise to the trypsin.
   [1913 Webster]

WordNet (r) 3.0 (2006):

trypsinogen
    n 1: inactive precursor of trypsin; a substance secreted by the
         pancreas and converted to active trypsin by enterokinase in
         the small intestine