HYDROLYSES OF PROTEINS. 81 



form in CONH; so according to TREAT B. JOHNSON * two analogous forms 

 of sulphur bondage exist in the proteins, namely the mercaptan form 

 SH as in cystine and the form NH.CH.CS.NH corresponding to the oxygen 

 binding in the polypeptids (see page 86). He has in fact also prepared 

 thio-polypeptides from glycocoll and these were analogous to the corre- 

 sponding glycin polypeptids (see page 88) and like certain proteins 

 gave H2S on acid hydrolysis. 



The constitution of the protein bodies is still unknown, although 

 the great advances made in the last few years have brought us very much 

 closer to the elucidation of the question. In studying the constitution 

 of the protein bodies they have been broken up in various ways into 

 simpler portions, and the methods used for this purpose have been of 

 different kinds. In such decompositions, for which only purified proteins 

 are to be used, first large atomic complexes proteoses and peptones 

 are obtained which still have protein characteristics, and these then 

 suffer further decomposition until finally we obtain simpler, generally 

 crystalline, or at least well-characterized, end products. 



As to the products obtained by hydrolytic cleavage with mineral acids, 

 important investigations have been carried out by numerous older and 

 more recent experimenters. 2 Besides certain acids, which will be men- 

 tioned later and which occur in few cases only, we obtain the following: 

 monamino-acids such as glycocoll, alanine, aminovaleric acid, leu- 

 cine, isoleucine, serine, aspartic and glutamic acids, cysteine and its disul- 

 phide cystine, phenylalanine, tyrosine, pyrollidine and oxypyrollidine 

 carboxylic acid, tryptophane and also the three hexone bases, histidine, 

 arginine and lysine, the two latter being diamino-acids. Besides these 

 also ammonia, sulphureted hydrogen, ethyl sulphide and melanoidins, 

 which latter seem to be secondary products, have been obtained. 



On the hydrolysis with alkalies we obtain, after a preliminary forma- 

 tion of intermediary steps which will be discussed later, chiefly the same 

 cleavage products as in acid hydrolysis but with the exception that in 

 the alkali hydrolysis a considerable part of the amino-acids become 

 racemerized and therefore appear in optically inactive form while in the 

 acid hydrolysis chiefly optically active acids are obtained. Because 

 of the action of the alkali a part may suffer further decomposition which 

 leads to the formation of simpler cleavage products and ammonia. 



On fusing proteins with caustic alkali, ammonia, methyl mercaptan and other 

 volatile products are evolved and other products are produced such as leucine, 



1 Journ. of biol. Chem., 9. 



2 In regard to the literature see O. Cohnheim, Chemie der Eiweisskorper, Braun- 

 schweig, 1911, and F. Hofmeister, Ergebnisse der Physiologie, Jahrg. I, Abt. 1, 759, 

 1902; E. Fischer, Untersuchungen iiber Aminosauren, Polypeptide und Proteine (1899- 

 1906), Berlin, 1906. See also special references. 



