proenzyme \pro"enzyme\, n. . bioch.
   any one of a class of proteins that are converted, in the
   normal course of cellular metabolism, into one or more active
   enzymes; also called zymogen. the conversion usually is due
   to a specific cleavage of a peptide bond by another enzyme,
   or may be due to acid.
   pjc
see also:
zymogen 

proenzyme
     n : any of a group of compounds that are inactive precursors of
         enzymes and require some change such as the hydrolysis
         of a fragment that masks an active enzyme to become
         active syn: zymogen
see also:
zymogen