CYSTINUKIA 517 



Baumann in collaboration with Preusse and Jaffe while working on 

 the mercapturic acids proved rather conclusively that cystin was a 

 disulphid. Even in their first researches with cystein, Baumann and 

 Preusse suggested that the graphic formula of this substance was 





H 2 N C SH 



COOH 



if it could be demonstrated that upon action with alkali, H 2 S, NH 3 and 

 pyroracemic acid are formed. It had been shown by Dewar and Gamgee 

 to their own satisfaction that pyroracemic acid could be formed from 

 cystin by action of nitric acid. But this "finding" could not be corrobo- 

 rated by Brenzinger, who worked in Baumann's laboratory, and the 

 formation of pyroracemic acid from cystin was shown to be an error 

 on the part of the English chemists. Baumann thought that pyroracemic 

 acid is an intermediary product in the decomposition of cystin. He, 

 therefore, wrote the graphic formulae of cystein and cystin thus : 



CH 2 CH 2 CH 2 



H 2 N C SH NH 2 C S S C NH 2 



COOH COOH COOH 



Cystein Cystin 



Corroborative evidence for this formula was added by Suter, who 

 found among the cleavage products of horn substance o-thiolactic 

 acid, which showed to be related as he thought to cystein, thus : 



CH 3 CH 3 



NH 2 C SH + H 2 == HC SH + NH 3 

 COOH COOH 



From the experiments of Suter, Baumann concluded that cystein is 

 derived from a-thio-aspartic acid, and that it (cystein) is the mother 

 substance of cystin, mercapturic acids and the thiolactic acid. 



Friedman (a), in 1902, working with cystin applied Jochem's finding 

 (that amino acids when treated with nitrous acid in hydrochloric acid 

 solution were converted into corresponding chloro derivatives) to cystin 

 and obtained dichlor-di-thio-propionic acid. Upon reduction, this sub- 

 stance gave p-thio-proprionic acid. From this Friedman concluded that 



