AMINO ACIDS 



315 



CHaCHNH.jCOOH, are strong adds, owing to the predomi- 

 nating influence of the two carboxyl groups, while the diamino 

 derivatives of the monocarboxylic acids, such as lysine 

 CH^NHaCH^CH.CHgCHNHXOOH, ornithine CHaNH^CH^ 

 CH2CHNH2COOH, etc., have strongly marked basic charac- 

 teristics, the two amino groups here overpowering the single 

 carboxyl group. 



A class of substances which have to be carefully distin- 

 guished from the amino acids are the acid amides. These are 

 derived from carboxylic acids by replacing the hydroxyl group 

 of the carboxyl by — NHj. Thus acetic acid CHgCOOH 

 gives the amide CH3CONH2 known as acetamide, while 

 aspartic acid COOHCH^CHNHgCOOH gives the amide 

 CONH2CH2CHNH,COOH known as asparagine. 



AMINO ACIDS OBTAINED AS CLEAVAGE PRODUCTS OF 

 PROTEINS. 



Mono-carboxylic 

 mono-amino acids. 



Dicarboxylic 

 mono-amino acids. 



(i) Aliphatic Covipounds. 



f Glycine or a-amino-acetic acid CH2NH0COOH 

 Alanine or a-amino-propionic acid CH3CHNH3COOH 

 Valine or o-amino-isovaleric acid 



CHoX 



^^/ )CH.CHNH2C00H 



CH3/ 



Leucine or a-amino-isocaproic acid 



^ j>CHCH2CHNH2COOH 



Isoleucine or a-amino-/3-methyl /3-ethyl propionic acid 



CH., \ 



' )CHCHNH2C00H 

 C2H5/ 

 Serine or a-amino j3-hydroxy propionic acid 

 CH.pHCHNHoCOOH 



Aspartic * or a-amino-succinic acid 



COOH CHXHNHoCOOH 

 Glutamic* or o-amino-glutaric acid 



COOH CHoCH^CHNHoCOOH 



* The amides corresponding to these two acids, namely asparagine 

 CONH2CH2CHNH2COOH and glutamine CONHaCHsCHjCHNH^OOH are 

 of considerable importance in plants. The former occurs in asparagus and is 

 produced in seeds which are allowed to germinate in the dark (Schulze, 

 " Landwirtsch. Gahrb.," 1878, 411), while the latter has been found in the 

 seeds of Cucurbita and many other plants (Schulze and Barbieri, " Ber. deut. 

 chem. Gesells.," 1877, 10, 199; Schul/e, id., i8g6, 29, 18S2). Asparagine and 

 glutamine being readily hydrolysed by mineral acids, are not obtained as cleavage 

 products of proteins by the ordinary methods of chemical hydrolysis, and for this 

 reason are not quoted in the above list of cleavage products. 



