158 . LECTURE VIII. 



By reduction, we obtain cysteine from it, which is an a-ammo-/3-thio- 

 propionic acid: 



CH 2 . SH 

 (NH 2 ) 



vyj-o.^ . 



AH. 



COOH 



Cysteine 



Cysteine, therefore, is closely related to alanine and serine. Friedmann * 

 oxidized cysteine and obtained cysteic acid: 



CH 2 . SO 2 . OH 

 (NH 2 ) 



X-'.*"*.^ 



CH< 



OOH 



Cysteic acid 



from which, by splitting off carbonic acid, we obtain taurine: 



CH 2 . S0 2 . OH 



CH 2 (NH 2 ) 



Taurine 



This indicated an important relationship between a product related to 

 taurocholic acid and cystine. The correctness of the formula of cystine 

 as presented by E. Friedmann, and soon after by C. Neuberg, 2 has recently 

 been strengthened by the synthesis of cystine by Erlenmeyer. 3 



Observations by Baumann and Preusse 4 do not harmonize with the 

 above formula. They found that when brombenzene was fed to a dog, 

 the excreted urine contained a compound containing bromine, nitrogen, 

 and sulphur in its composition. Its composition was CnH^BrNSOs. 

 Baumann and Preusse designated this compound: Bromphenyl mer- 

 capturic acid. From this, acetic acid and a compound, CgHioBrNSO 2 , 

 are obtained by hydrolysis. The latter formula corresponds to the 

 empirical formula of cysteine, if the bromphenyl residue is replaced by 

 a hydrogen atom. The compound formed together with acetic acid was 

 therefore considered as bromphenyl cysteine. From the resulting cleavage- 



1 E. Friedmann: Hofmeister's Beitr. 3, 1 (1902). 



3 C. Neuberg: Ber. 36, 3161 (1902). Cf. K. A. H. Morner: Z. physiol. Chem. 42, 

 349 (1904). 



8 Erlenmeyer: Jr. Ber. 36, 2720 (1903). 



4 E. Baumann and C. Preusse: ibid. 12, 806 (1879); Z. physiol. Chem. 6, 309 (1881). 



