POLYPEPTIDES. 85 



amino-acid unites with the carboxyl group of the other. In accord with 

 this behavior we can, as HOFMEISTER l has explained, but which was first 

 proven by the epoch-making investigations of EMIL FISCHER, consider 

 the proteins as chiefly formed by the condensation of amino-acids, where 

 the amino-acids are united to each other by means of imino-groups 

 according to the following scheme: 



NH.CH.CO NH.CH.CO NH.CH.CO NH.CH.CO 



II II 



C 4 H 9 CH 2 .C 6 H 4 (OH) CH 2 .COOH C 3 H 6 .CH 2 .NH 2 



(Leucine) (Tyrosine) (Aspartic acid) (Lysine) 



Closely connected with this conception is the question whether it is 

 possible to prepare protein-like substances synthetically. In this con- 

 nection we must mention that GRIMAUX and later also SCHUTZENBERGER 

 and PICKERING have been able to prepare substances, which in many 

 properties are similar to the proteins, from various amino-acids either 

 alone or mixed with other bodies such as biuret, alloxan, xanthine, or 

 ammonia. Of special interest are the investigations of CURTIUS and his 

 collaborators, in which they were able to prepare synthetically the so- 

 called biuret base (triglycyl-glycine ethyl ester) and subsequently many 

 Other bodies which were related to the proteins. The most important 

 work on the chaining of amino-acids has. been performed by E. FISCHER 2 

 and his pupils. They have prepared a large number of complex bodies 

 called polypeptid'es, which according to whether they contain two or 

 more amino-acid groups united together, are called di-, tri.-, tetrapeptides, 

 etc. As examples of polypeptides we will mention dipeptides: glycyl- 

 alanine, leucyl tyrosine, propylalanine, diaminopropionic-acid dipepti.de, 

 lysyl-lysine, histidyl-histidine ; leucyl-histidine ; tripeptides: diglycyl- 

 glycine, leucyl -alanyl-gly cine, dileucylcystine ; tetrapeptides: triglycyl- 

 glycine, dileucyl-glycyl-glycine ; pentapeptides : tetraglycyl-glycine, and 

 leucyl-triglycyl-glycine ; hexa and heptapeptides: leucyl-tetraglycyl- 

 glycine and leucyl-penta glycyl-glycine respectively. The most complex 

 polypeptide thus far prepared is an octodecapeptide with 15 glycocoll 

 and 3 leucine residues namely: Z-leucyltriglycyl-Z-leucyltriglycyl-Z-leucyl- 

 octoglycylglycine = NH 2 CH(C 4 H 9 )CO. [NHCH 2 CO] 3 . NHCH (C 4 H 9 ) CO. 

 [XHCH 2 COl 3 .NHCH(C 4 H9)CO.fNHCH 2 CO] 8 .NHCH 2 COOH. with the sup- 



1 " Ueber den Bau des Eiweissmolekiils." Gesellsch. deutsch. Naturforscher und 

 Aertze, Verhandl. 1902, and Ergebnisse der Physiologie, Jahrg. I, Abt. 1, 759. 



3 See Pickering, King's College, London, Physiol. Lab. Collect. Papers, 1897, which 

 also cites Grimaux's work; also Journ. of Physiol., 18, and Proceed. Roy. Soc., 60, 

 ls'.)7; Schiitzenberger, Compt. rend., 106 and 112; Curtius, Journ. f. prakt. Chem. 

 (X. P.), 26 and 70, and Ber. d. d. chem. Gesellsch., 37; Fischer and collaborators, 

 Untersuchungen iiber Aminosauren, Polypeptide und Proteme (1899-1906) and Ber. 

 d. d. chem. Gesellsch., 39, 40, 41 and Annal. d. Chem. u. Phann., 354, 357, 363. 



