194 EMIL L. SMITH, ROBERT L. HILL AND J. R. KIMMEL [11 



its jV-terminal end, both because yV-terminal isoleucine disappears and be- 

 cause new end groups are found. Inasmuch as the hydrolysis by the amino- 

 peptidase proceeds in a stepwise manner, it is to be anticipated, as the results 

 in Table 6 demonstrate, that a more and more complex mixture of end 

 groups will appear as more breakdown occurs. For this reason, study of 

 end groups formed beyond the level indicated in Table 6 has not been 

 pursued. 



Table 6 

 AMINO END GROUPS OF DEGRADED MERCURIPAPAIN 



* indicates present, but not quantitatively estimated. 



Amino acids liberated. At various stages of hydrolysis of mercuripapain by 

 the aminopeptidase, amino acid analyses have been performed. The free 

 amino acids were collected by dialysis and analyzed on ion-exchange columns 

 by the older method of Moore and Stein^^ or by a modification of the newer 

 method of Spackman, Moore and Stein. ^^ In no case was there any evidence 

 for the presence of unexpected peaks which might be due to liberated pep- 

 tides. Representative results at two stages of degradation are given in 

 Table 7. Other results are presented in Table 8 and will be discussed below. 

 It should be emphasized that at no point does the relative composition 

 of the liberated amino acids resemble that of papain or of the aminopepti- 

 dase. The data indicate that the composition of the iV-terminal portion of 



