60 CHEMISTRY OF THE PROTEIDS CHAP. 



therefore, have the constitutional formula given on p. 57. These 

 authors distinguished in their first paper between two distinct cystins : 

 one occurring in cystin-stones is a-thio-yS-amino-propionic acid, while 

 the other found in proteids is a-amino-/3-thiopropionic acid. That 

 these two cystins really exist is clearly shown by the researches of 

 Loewy and Neuberg, 1 who find that the cystin occurring in cystinuria 

 is protein- or horn-cystin, and is not stone-cystin. They suggest, in 

 following Baumann's view, 2 that in the albumin-molecule a carboxy- 

 cystein (or carboxy-cystin) exists which is a thio-amino-succinic acid, 

 which, according to the place where C0 2 is split off, gives rise either 

 to proteid-cystin or to stone-cystin. 



COOH COOH 



CH 2 SH CH 2 SH CH . SH 



I - I ~> I 



CH . NH 2 CH . NH 2 CH, . NH 2 



I I 



COOH COOH 



Protein-cystein. Carboxy-cy stein. Storie-cystein. 



E. Erlenmeyer, 3 jun., then succeeded in preparing, synthetically, 

 a-amino-/?-thiopropionic acid, and from it cystin. Morner 4 found 

 thiolactic acids to be converted into the disulphides by gentle oxida- 

 tion ; treating, e..g., a watery solution of a-thiolactic acid with ferric 

 chloride or iodine, yields a-dithiodilactylic acid, which is very soluble 

 in water, while /3-dithiodilactylic acid is much less soluble. Morner 

 was the first to state .that there exist not only stereo-isomeric, but 

 also structurally isomeric cystins and cysteins. In cystin pre- 

 pared from human hair and filings of cows' horns both /3-amino- 

 a-thiolactic acid and a-amino-/3-thiolactic acid exist, perhaps even in 

 equal quantities. On being decomposed the a-amino-/3-thiolactic acid 

 gave rise to sulphuretted hydrogen and alanin, while /3-amino-a-thio- 

 lactic acid gave rise to ammonia and a-thiolactic acid. Oxidation may 

 also take place simultaneously, and so cystin be formed from cystein, 

 or the disulphide from thiolactic acid. In this paper Morner gives a 

 full account of how to test for the two thiolactic acids and also the 

 best methods for their preparation. Morner 5 does not believe a-thio- 



1903. Quoted by J. Wohlgemuth in Zeitschr.f. physiol. Chem. 40. 32 (1903), and ibid. 

 44. 472 (1905). 



1 A. Loewy and C. Neuberg, ibid. 43. 338 (1904). 



2 Baumann, ibid. 2O. 583 (1895). 



3 E. Erlenmeyer, jun., Ber. d. deutsch. chem. Ges. 36. 2720 (1903). 



4 K. A. H. Morner, Zeitschr. f. physiol. Chem. 52. 349 (1904). 



5 K. A. H. Mbruer, ibid. 52. 365 (1904). 



