3.4.22.2	no modification	nonglycosylated enzyme	95685	
3.4.22.2	proteolytic modification	the proenzyme is activated by cleavage of the prosegment	667324	
3.4.22.2	proteolytic modification	the zymogen of papain contains a pro-peptide at the N-terminus of the catalytic domain. Pro-peptide contains residues which act as pH-sensors in zymogen activation cascade. The conserved Asp72 residue of the pro-peptide, is a highly conserved residue of the GXNXFXD motif that is an important pH sensor in the zymogen activation process and the pro-peptide part can also be a useful target of protein engineering for altering the activation pH of a protease	753357	
3.4.22.2	side-chain modification	propapain is a thio-containing but catalytically inactive protein, that is a structural isomer of papain that can be transformed into papain by thiol-disulfide interchange initiated by addition of a suitable nucleophile such as thiolate	95707	
3.4.22.2	side-chain modification	propapain is activated by intramolecular thiol-disulfide exchange which is catalyzed by cysteine	95681	
3.4.22.2	side-chain modification	the enzyme is produced as an inactive precursor	95685