PRIMARY DISSOCIATION-PRODUCTS 59 



SH 



CH 3 C COOH. 



That the SH and the NH 2 radicals are not attached to the same 

 C atom was first shown by C. Neuberg l and E. Friedmann. 2 Neuberg 

 prepared issethionic acid by oxidising cystein directly with nitric acid. 

 Istethionic acid bears to taurin the same relation as does an oxy-acid 

 to an amino-acid. 



CH 2 .S0 3 H CH 2 .S0 3 H 



CH 2 .OH CH 2 .NH 2 



Isnethionic acid. Taurin. 



Friedmann oxidised cystein to amino-sulpho-propionic acid, and the 

 latter by removal of C0 2 into taurin : 



CH 2 .SH CH 9 .S0 3 H 



| CH 9 .S0 3 H 



CH.NH 2 -> CH.NH, --> | 

 | | CH 2 .NH 2 



COOH COOH 



Cystein. Amino-sulpho-propionic acid. Taurin. 



.Cystin is laevo-rotatory, but being an amino-acid it becomes partly 

 racemised when it is acted upon by acids ; these two cystins Morner 

 showed to differ from one another also in other properties, for the 

 active cystin crystallised in six-sided plates, while the inactive cystin 

 formed needles resembling ty rosin, which substance also frequently 

 accompanies cystin. 3 Morner prepared cystin by decomposing horn 

 filings or human hair with hydrochloric acid, removing the acid, 

 crystallising out the cystin and tyrosin, and finally separating these 

 by means of fractional crystallisation. Patten precipitated it with 

 mercuric sulphate dissolved in sulphuric acid. 



In his second paper Friedmann 2 stated cystin to be a-diamino-/3- 

 dithio-dilactylic acid. 



S . CH 2 CH . NH 2 CO . OH 

 S . CH 2 CH . NH 2 CO . OH. 



This formula corresponds, therefore, to the one given subsequently 

 by Neuberg and Mayer 4 to their 'protein-cystin.' Cystin would, 



1 C. Neuberg, Ber. d. deutsch. chem. Ges. 35. 3161 (1902). 



2 That optically active stone-cystin also crystallises in needles has already been 

 pointed out when comparing protein- and stone-cystins on p. 57. 



3 E. Friedmann, Hofineister's Beitr. 2. 433, and 3. 1 (1902). 



4 C. Neuberg and P. Mayer, Vortrag in d. d. chem. Gesellsch. zu Berlin, May 25, 



