THE CHEMISTRY OF ALBUMINS 199 



Pyrollidin-carboxylic Acid or Prolin 



This lias been obtained as a product of hydrolysis of casein 

 and is of interest from the point of view of the synthetical 

 experiments of Emil Fischer and others. It has the follow- 

 ing constitution : — 



H9C CH2 



H,C^ 



^CH— COOH 



/ 



NH 



Sulphur Bodies 



Cystin. — This is a very interesting substance as it is prob- 

 ably the parent body of the isomeric forms a-cystin and 

 /8-cystin, which are very likely the parent bodies of the un- 

 pleasant smelling sulphur derivatives of albumin. These two 

 bodies are dilierentiated according to the products obtained 

 when they are treated with hydrochloric acid under pressure, as 

 indicated by the following formulas : — 



CH2SH-CHNH3-COOH ^ CH2-CHNH2-COOH+H2S 



o-cystin — > a-alanin 4- sulphuretted 



hydrogen 



CH2NH2-CHSH-COOH ^ CH3-CHSH-COOH+NH3 



^-cystin a-thiolactic acid + ammonia 



Probably both a- and /3-cystin contain at least two groups 

 as given in the above equations, joined in each case by sulphur 

 thus : — 



SCH^-CHNHs-COOH CHoNH^-CHS-COOH 



SCH,-CHNH,-COOH CH^NH^-CHS-COOH 



a-cystin j3-cystin 



