NATURAL POLYPEPTIDES. 89 



tion to the fact that a hj-drolysis of polypeptides as well as proteins by 

 the same enzymes with the splitting off of amino-acids is not sufficient 

 evidence that the proteins contain the same form of amino-acid chains 

 as the polypeptides. 



We have also a very important support for this view in the fact that 

 polypeptides occur in the cleavage products of the proteins. This is, 

 to a certain extent, the reverse of the above-mentioned syntheses. After 

 FISCHER and BERGELL were able to isolate from the cleavage products 

 of silk fibroin a dipeptide in the form of an anhydride which seemed 

 to be a glycylalanine, FISCHER and ABDERHALDEN 1 further studied 

 this question, and by the partial hydrolysis of fibroin obtained not 

 only the above-mentioned polypeptide, which they showed was glycyl- 

 d-alanine anhydride, but also glycyl-/-tyrosine anhydride, and they 

 established the identity by the correspondence with the synthetically 

 prepared bodies. From elastin they obtained glycyl-Z-leucine anhydride, 

 Z-leucyl-d-alanine anhydride, glycyl-d-valine anhydride and a dipep- 

 tide anhydride which yielded d-alanine and Z-proline on hydrolysis. 

 They have also shown the presence of other polypeptides among the 

 hydrolytic products; we especially mention one tetrapeptide obtained 

 from fibroin which consisted of 2 molecules glycocoll, 1 molecule d- 

 alanine and 1 molecule Z-tyrosine. This tetrapeptide gave the biuret 

 reaction and also Millon's reaction. It was precipitated by tannic acid, 

 by saturated ammonium sulphate solution, and by NaCl in the presence 

 of free acid, and in many regards behaved like a proteose. 



Polypeptides have also been found by other investigators in the hydro- 

 lytic cleavage products of proteins. Thus LEVENE with WALLACE and 

 BEATTY isolated a glycyl-Z-proline anhydride from gelatin after tryptic 

 digestion, and LEVENE and BEATTY have shown the presence of a lysyl- 

 glycyl peptide among the tryptic cleavage products of ovalbumin. OS- 

 BORNE and CLAPP 2 obtained from a plant protein, gliadin, a crystalline 

 dipeptide which yielded phenylalanine and proline on cleavage. 



We have therefore conclusive basis for the assumption that in the 

 proteins, peptide bindings chiefly occur, i.e., a combination of the a- 

 ainino-acids by means of the imide binding. It is also possible that 

 other bindings may occur, and FISCHER has also given expression to such 

 a possibility. Besides the above-mentioned imide binding another kind 

 must also without doubt exist in the proteins, namely, the anchoring 

 of the urea-forming group (the guanidine residue) with the ornithin 



1 Fischer and Bergell, see Bicohem. CentralbL, I, p. 84. Fischer and Abderhalden, 

 Sitz. Ber. d. k. Acad. d. Wissensch., 30 (1907) and Ber. d. d. chem. Gesellsch. 39 and 40. 



2 Levcne and Wallace, Zeitschr. f. physiol. Chem., 47; Levene and Beatty, Ber. 

 d. d. chem. Gesellsch., 39, and Biochem. Zeitschr., 4; Osborne and Clapp, Amer. Journ. 

 of Physiol., 18. 



