518 



KAHN AND ROSENBLOOM 



the sulphur atom Avas in the (3 position. He now investigated whether 

 the amino group was in the a or (3 position. Upon oxidizing cystin 

 with bromin, Friedman obtained cysteinic acid which would be either 



CH 



SO 3 H 



or 



CH 5 



COOH 



CH 2 SO 3 H 

 CHNH 2 

 COOH 



But upon heating this acid he obtained taurin, and this change could 

 be explained only by the fact that cysteic acid has the formula : 



CH SOH 



CH NH 2 



COOH 



Cysteic acid 



CH 2 SO 3 H 



CH 2 NH 2 



Taurin 



In the same year (1902), Carl Neuberg also demonstrated that the 

 sulphur and the nitrogen in cystein were attached to different carbon 

 atoms. He treated cystin with nitric acid, which pointed to the correct- 

 ness of Friedman's formula : 



CH SH 



CH 



COOH 



Cystein 



CH SOH 



CH NH 2 



COOH 



Cysteic Acid 



CH 2 S0 3 H 



CH 2 OH 

 Isothionic Acid 



From these reactions it is seen that cystin might be a precursor of 

 taurin. 



Cystin occurs in the protein molecule in union with the other amino 

 acids. Quantitative analyses of the cystin fraction have yielded the 

 following figures : 



Globulin of hemoglobin (horse's blood) 0.3% 



Egg albumin 0.3 



Crystalline egg albumin ? 



Serum albumin from horse's blood 2.5 



Serum globulin from horse's blood 1.5 



Fibrin . 1.1 



