86 THE PROTEIN SUBSTANCES. 



that in the hydrolysis certain carbon nuclei may be secondarily formed 

 from others. Even if we. admit the above, still it is undoubtedly true 

 that the chief cleavage products of the protein substances are amino- 

 acids. EMIL FISCHER has shown that the amino-acids have the property 

 of readily grouping together when water is split off and the amide group 

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

 accord with this behavior we can, as HOFMEISTER 1 and others have 

 explained, but which was first proved by the epoch-making investiga- 

 tions 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- 



C 4 H 9 CH 2 .C 6 H4(OH) CH 2 .COOH 



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



Such chaining of animo-acids is for the synthesis of protein-like bodies 

 of the very greatest importance. The older statements of GRIMAUX, 

 SCHUTZENBERGER and PICKERING on the artificial preparation of pro- 

 tein-like substances where these investigators were able to prepare sub- 

 stances, 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 syn- 

 thetically the so-called biuret base (triglycyl-glycine ethyl ester) and sub- 

 sequently many other bodies which were related to the proteins. The 

 most important work on the chaining of amino-acids has been per- 

 formed by E. FISCHER 2 and his pupils but especially by ABDERHALDEN. 

 They have prepared a large number of complex bodies called polypeptides 

 by FISCHER, 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- 

 tyrosine, alanylglycine, leucylglycine, leucylcystine, prolylphenylalanine, 



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

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



2 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, 

 1897; Schiitzenberger, Compt. rend., 106 and 112; Curtius, Journ. f. prakt. Chem. 

 (N. F.), 26 and 70, and Ber. d. d. chem. Gesellsch., 37; Fischer and collaborators, 

 Untersuchungen iiber Aminosauren, Polypeptide und Proteiine (1899-1906) Berlin 1906 

 and Ber. d. d. chem. Gesellsch., 39, 40, 41, 42, and Annal. d. Chem. u. Pharm., 354, 

 357, 363, 365, 369, 375; see also Abderhalden, Ber. d. d. chem., Gesellsch, 40 to 43 and 

 Zeitschr. f. physiol. Chem., 72, 75, 77. 



