11] STRUCTURE AND ACTIVITY OF PAPAIN 195 



Table 7 



AMINO ACIDS LIBERATED FROM MERCURIPAPAIN BY 

 AMINOPEPTIDASE 



Preparation I = approximately 19 residues released; Preparation 11= approximately 72 

 residues released 



tlie papain molecule is different from that of the C-terminal region. It is 

 striking that much of the threonine, alanine, leucine and isoleucine are in 

 the first 72 residues, whereas most of the tyrosine and valine residues appear 

 to be in the remainder of the molecule. It is particularly noteworthy that only 

 one of the six cysteine residues has been located in the A^-terminal region. 

 Obviously this cannot be the enzymically active residue. 



It is noteworthy that when 19 residues are released, there appears to be 

 excellent stoichiometry, indicating a rather uniform hydrolysis of all mole- 

 cules. In contrast to this, when approximately 72 residues are released, the 

 breakdown is no longer uniform in accord with results obtained by the 

 DNP method on residual mercuripapain. 



Although we have performed analyses of the liberated amino acids be- 

 yond the stage given in Table 7, we are uncertain as to the significance of 

 these results at the present time. There is some suspicion that slight activa- 

 tion of mercuripapain may occur in the presence of the large amounts of 

 aminopeptidase required for such extensive degradation. Moreover, the 

 large amounts of free amino acids may cause also activation of the pro- 

 teinase. Until such results are adequately controlled we prefer to present 

 only the results of experiments in which it is certain that such complicating 

 factors do not occur. 



