11] STRUCTURE AND ACTIVITY OF PAPAIN 187 



7 days. The hydrolysate was worked up in the usual manner and subjected 

 to electrophoresis on paper in acetic acid at pH 2-3 or passed through 

 Dowex-50x4 in the hydrogen cycle. The strongly acidic fraction was ob- 

 tained by both methods. The peptides containing cysteic acid could then 

 be separated by two-dimensional paper chromatography. The peptides iso- 

 lated by this procedure, whose structure has been completely or partly 

 elucidated, are listed in Table 2. Obviously, these few peptides do not 

 account for all of the sequences involving cysteic acid which must be pre- 

 sent in the oxidized protein, probably because neutral peptides, i.e., those 

 containing cysteic acid and a basic residue, would not be isolated by the 

 methods employed. 



It is evident that the fragmentary data of Table 2 give little information 

 by themselves and no clue is obtained as to which one of these sequences, 

 if any, may be concerned in the enzymic activity. 



Amino acid composition. The composition of papain is given in Table 3.^* 

 Estimation of most of the amino acids was performed by chromatography 



Table 2 



CYSTEIC ACID PEPTIDES DEFINITELY 



IDENTIFIED FROM PARTIAL HYDROLYSATES 



OF OXIDIZED PAPAIN" 



Asp. CySOgH 

 Ser. CySOgH 

 Val. CySOgH 

 Gly (Pro, CySOgH) 



CySOgH. Asp 



CySOgH. Gly 



CySOg. Gly. Asp 



Ser. CySOsH. CySOgH (?) 



Table 3 

 AMINO ACID COMPOSITION OF PAPAIN".^* 



