Berger A, Schechter I (1970). "Mapping the active site of papain with the aid of peptide substrates and inhibitors". Philos. Trans. R. Soc. Lond., B, Biol. Sci.257 (813): 249–64. PMID4399049. doi:10.1098/rstb.1970.0024.
Dryer.J.W.,Neurath.H. The Activation of Chemotyrpsinogen: ISOLATION AND IDENTIFICATION OF A PEPTIDE LIBERATED DURING ACTIVATION Department of Biochemistry, University of Washington [1955]http://www.jbc.org/content/217/2/527.full.pdf [accessed Oct. 10, 2012]
Berger A, Schechter I (1970). "Mapping the active site of papain with the aid of peptide substrates and inhibitors". Philos. Trans. R. Soc. Lond., B, Biol. Sci.257 (813): 249–64. PMID4399049. doi:10.1098/rstb.1970.0024.