THE CHEMISTRY AND PHYSICS OF THE CELL 21 



8. Tyrosin, HO< >CH 2 -CH COOH. 



/NH 2 



. /CH,-CH-COOH. 

 9. Tryptophan, 1 



These three substances represent the aromatic constituents of 

 the proteid molecule, and differ from the simpler amino-acids 

 merely in the presence of the benzene ring. 



10. a-pyrrolidin carboxylic acid (prolin), 

 H 2 C CH COOH. 



1 1 . Oxy-a-pyrrolidin carboxylic acid 2 (oxy-prolin), 

 H 2 C CH 2 



(?) HO HC CH COOH. 

 NH 



Both of these substances lie under the suspicion of being 

 formed from some other amino-acid through re-arrangement 

 within the molecule during the process of cleavage, but this 

 idea has not been positively established, and they are among 

 the most constantly obtained of the cleavage products. 



12 Serin /OH/NH, 







CH CH COOH. 



This substance, together with oxy-0-pyrrolidin carboxylic 

 acid, is important as being an oxy-acid, which brings the proteid 

 molecule into close relation with the carbohydrates. Amino- 

 compounds even more closely related to the carbohydrates have 

 occasionally been isolated (glucosamin) and it is possible that 

 they are frequently present in proteids. 



NH, 

 _ ^ _ ^ _ ^ _ CH _ COOH> 



NH NH 



"1 A A * * II / "^^2 



1D ' H 2 N C NH CH 2 CH 2 CH 2 CH COOH. 



1 The exact structure of tiyptophan has not been finally determined ; the 

 above formula, that of El linger, seems to be most probably the correct one. 



2 The position of the OH group in oxy-prolin has not yet been finally 

 determined 



/ 2 /, 



13. Lysm, 



