198 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



guanidine-a-amino- valerianic acid ; guanidine has the formula 

 NH=C(NH2)2, and arginin, therefore, may be written 



NH2 NHj 



I H H H I 



NH= C— N— C— C— C-C— C 

 H H H H H \ 



OH 



Ai'ginia is really a compound of guanidine with ornitJiin a 

 derivative of which is found in the urine of birds. Ornithin 

 is a-S-di-amino-valerianic acid. 



Lysin is a-e-di-amiao-normal-caproic acid, i.e. 

 CH2NH2C2CH2CH2CH2CHNH2CO2H 

 It occurs in greatest quantities in casein and gelatine. 



Histidin has a rather more complex constitution than 

 either of the other two hexone bases. It is probably a 

 condensation product formed by elimination of NII3 from 

 arginin and its constitutional formula may be provisionally 

 written thus : — 



CH— N ^, 

 I /CH 



C— HN 



CH— NHo 

 COOH 



Amino-dicarboxylic Acids 



Of these the following may be mentioned, aspartic acid or 



CHNHoCOjH 

 amino-succinic acid, | , and glutaminic acid or 



CH2CO2H 

 a-amino-glutaric acid, COOHCHNHjCHjCHjCOsH. 



