AMINO ACIDS 



305 



CH.^jCHNHXOOH, are strong acids, owing to the predomi- 

 nating influence of the two carboxyl groups, while the diamine 

 derivatives of the monocarboxylic acids, such as lysine 

 CH2NH2CHXH2CHXHNH2COOH, ornithine CH.NHaCHa 

 CH^CHNH.COOH, 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 arc the acid amides. These are 

 derived from carboxylic acids by replacing the hydroxyl group 

 of the carboxyl by — NH.2. Thus acetic acid CH3COOH 

 gives the amide CHgCONH.^ known as acetamide, while 

 aspartic acid COOHCHgCHNH^COOH gives the amide 

 CONHaCHoCHNH.COOH known as asparagine. 



Mono-carboxylic 

 mono-amino acids. 



Dicarboxylic 

 mono-amino acids. 



^CH . CHNHXOOH 



AMINO ACIDS OBTAINED AS CLEAVAGE PRODUCTS OF 

 PROTEINS. 



(i) Aliphatic Compounds. 



Glycine or o-amino-acetic acid CHjNHoCOOH 

 Alanine or o-amino-propionic acid CHjCHNHjCOOH 

 Valine or o-amino-isovaleric acid 



CH3^ 



CH3, 

 Leucine or a-amino-isocaproic acid 



^^^^CHCHaCHNH^COOH 



Isoleucine or o-amino-;8-methyl ^-ethyl propionic acid 



CH \ 



^ )CHCHNHXOOH 



Serine or a-amino ;8-hydroxy propionic acid 

 CH2OHCHNH2COOH 



(Aspartic * or o-amino-succinic acid 

 COOH CR^CHNHaCOOH 

 Glutamic* or a-amino-glutaric acid 

 COOH CH2CH2CHNH2COOH 



* The amides corresponding to these two acids, namely asparagine 

 CONH2CH2CHNH2COOH and glutamine CONH0CH2CH2CHNH2COOH 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 Cuciirbita and many other plants (Schulze and Barbieri, " Ber. deut. 

 chem. Gesells.," 1877, 10, 199 ; Schulze, id., 1896, 29, 1882). 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. 

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