30 NUTRITION OF FARM ANIMALS 



C. Diaminomonocarboxylic acids 



12. Arginin, C 6 Hi4N 4 O 2 , or a-amino-y-guanidin valerianic acid. 



HN=C/ NH2 



NH CH 2 CH 2 CH 2 CH(NH 2 ) COOH 



13. Lysin, CoHi 4 N 2 O 2 or a, e-diaminocaproic acid. 



H 2 N CH 2 CH 2 CH 2 CH 2 CH(NH 2 ) COOH 



D. Heterocyclic compounds 



14. Histidin, CeHgNsO^ or /S-imidazol-a-aminopropionic acid. 



CH 



^ \ 



N NH 



I I 



CH = C CH 2 CH(NH 2 ) COOH. 



15. Prolin, C 5 H 9 NO 2 , or -pyrrolidin carboxylic acid 



CH 2 CH 2 



I I 



CH 2 CH COOH 



\ / 

 NH 



1 6. Oxyprolin, or oxypyrrolidine carboxylic acid. 



C 5 H 9 N0 3 



17. Tryptophan, CnHt 2 N 2 O 2 , or jS-indol-a-aminopropionic acid. 



C CH 2 CH(NH 2 ) COOH 



/\ 

 C C H 4 CH 



\ / 

 NH 



48. Synthesis of proteins. Peptids. Fischer and others 

 have shown that the amino acids which result from the cleavage 

 of the simple proteins may combine with each other, the NH2 

 of one uniting with the COOH group of the other with the 

 elimination of one molecule of water. As many as 18 molecules 

 of amino acids have been combined in this way, although the 

 exact structure of the resulting compounds is still more or less 

 uncertain. 



The compounds of the amino acids which have been prepared 

 artificially have received the general name of peptids, the pre- 

 fixes di-, tri-, etc., being used to indicate the number of amino 

 acid molecules entering into the compound. The term poly- 



