THE SYNTHESIS OF THE PROTEINS 45 



the acyl radical, as in alanyl-glycine, alanyl-alanine, alanyl-leucine, 

 hydrolysis occurred, but the reverse happened when leucine, valine or 

 aminobutyric acid were the acyl radicals; in the three cases, leucyl- 

 alanine, leucyl-glycine and leucyl-proline, no hydrolysis took place ; 

 here the racemic compound was employed and the resistance might have 

 been due to this factor, but the instance of 1-leucyl-glycine appears to 

 confirm the older result. 



If tyrosine, isoserine and cystine stood at the end of the chain, 

 trypsin hydrolysed the compound ; in the only case examined where 

 tyrosine, combined with /3-naphthalene-sulphonic acid, acted as the acyl 

 radical, there was no hydrolysis. 



2. The Configuration of the Molecule. 



This is of the greatest importance for a polypeptide to be hydrolysed 

 by trypsin, as will be seen from the list of compounds published in 

 1907. Only those compounds containing the naturally occurring 

 optically active variety of the amino acid are hydrolysed by trypsin. 



The compounds marked with an asterisk are racemic and their 

 hydrolysis was effected asymmetrically, only that portion of the molecule 

 containing the natural stereoisomer being attacked. This explained the 

 difference between alanyl-leucine A and alanyl-leucine B ; the former 

 probably consisted of d-alanyl-1-leucine + 1-alanyl-d-leucine, the first of 

 which contains the natural stereoisomers upon which the hydrolysis 

 depends ; the latter would consist of d-alanyl-d-leucine + 1-alanyl-l- 

 leucine. The later experiments of 1907 proved this supposition. It is 

 more noticeable in the case of leucyl-leucine, which must have been 

 1-leucyl-d-leucine + d-leucyl-1-leucine since 1-leucyl-l-leucine is hydrolysed. 



3. The Number of Amino Acids. 



Only the various polypeptides containing several glycine radicals 

 come at present under this heading. Several interesting details are at 

 once apparent. Hydrolysis first took place when five glycine radicals, 

 as in tetraglycyl-glycine, are combined together, although it occurred 

 in the ester of triglycyl-glycine, or the biuret base of Curtius, which had 

 been previously examined by Schwarzschild. The length of the glycine 

 chain is therefore of importance, but an alteration in the carboxyl group 

 may have an influence ; it is worth noting that Warburg observed that 

 leucine ester was hydrolysed by pancreatic juice, but whether this was 

 due to the trypsin or the lipase in the juice has not yet been determined. 



The fact that leucyl-glycyl-glycine was hydrolysed, but not the more 

 complex dileucyl-glycyl-glycine, was probably due to the configuration 

 of the dileucyl group. 



4. The Nature of the Enzyme. 



