THE COMPONENTS OF PLANTS AND ANIMALS 29 



The amino acids derived from the proteins may be divided 

 into two classes ; the monamino acids, of which glycin is typi- 

 cal, containing one NH 2 group, and the diamino acids, contain- 

 ing two NH 2 groups. To these there are to be added certain 

 heterocyclic compounds. Plimmer 1 gives the following list of 

 the amino acids which have been identified with certainty among 

 the cleavage products of the proteins. The presence of others 

 has been claimed by several investigators. 



A. Monoaminomonocarboxylic acids 



1. Glycin, C 2 H 5 NO 2 , or aminoacetic acid. 



CH 2 (NH 2 ) COOH 



2. Alanin, C 3 H 7 NO 2 , or a-aminopropionic acid. 



CH 3 CH(NH 2 ) COOH 



3. Valin, C 5 HnNO 2 , or a-aminoisovalerianic acid. 



CH 3 \ 



^CH CH(NH 2 ) COOH 

 CH 3 / 



4. Leucin, C 6 Hi 3 NO 2 or a-aminoisocaproic acid. 



CH 3 \ 



CH CH 2 CH(NH 2 ) COOH 

 CH 3 / 



5. Isoleucin, C 6 Hi 3 NO 2 , or a-amino-/3-methyl-/3-ethyl-propionic acid. 



CH 3 \ 



CH CH(NH 2 ) - COOH 

 C 2 H 5 / 



6. Phenylalanin, C 9 HnNO 2 , or /3-phenyl-a-aminopropionic acid. 



C 6 H 5 CH 2 CH(NH 2 ) COOH 



7. Ty rosin, C 9 HnNO 3 , or 0-parahydroxyphenyl-a-aminopropionic 

 acid. HO C 6 H 4 CH 2 CH(NH 2 ) COOH 



8. Serin, C 3 H 7 NO 3 , or 0-hydroxy-a-aminopropiomc acid. 



CH 2 (OH) CH(NH 2 ) COOH 



9. Cystin, C 6 Hi 2 N 2 O 4 S 2 , or dicysteine, or di- (/3-thio-a-aminopro- 

 pionicacid) HOOC CH(NH 2 ) CH 2 S S CH 2 CH(NH 2 ) COOH 



B. Monoaminodicarboxylic acids 



10. Aspartic acid, C^rNO^ or a aminosuccinic acid. 



HOOC CH 2 CH(NH 2 ) COOH 



11. Glutamic acid, C 5 H 9 NO 4 , or a-aminoglutaric acid. 



HOOC CH 2 - CH 2 CH(NH 2 ) COOH 



1 The Chemical Constitution of the Proteins, Part I, ad Ed., 1912. 



