44 PROTEINS. 



laws which are not fully known. This may perhaps be due to 

 the hydrolysing effects of the acid combined with those of other 

 hydrolysts taking a course influenced by both of them. 



Fischer separates the amino -acids obtained by long boiling with 

 acids by esterifying, crystallising out the glycine ester, and dis- 

 tilling the others in vacuo, and extracting with ether. Fischer 

 and Bergell also convert the amino-acids into their /2-naphthalene 

 sulphonates, which are very slightly soluble. These methods 

 involve, however, some loss, but they give a rough estimate of 

 the proportions of the amino-acids. 



A large number of amino-acids have been separated from the 

 products of continued hydrolysis of proteins ; these are 



A. Mono -amino -mono -carboxy lie acids. 



Amino-acetic acid, or glycine. 

 Amino-propionic acid, or alanine. 

 Amino -butyric acid. 

 Amino -valeric acid or valine. 

 Iso-butyl-amino-acetic acid, or leucine. 



B. Hydroxy-mono-amino-mono-carboxylic acids. 



Hydroxy-amino-propionic acid, or serine. 

 Tetra-hydroxy-amino-caproic acid. 



C. Mono-amino-di-carboxylic acids. 



Amino -succinic acid, or aspartic acid. 

 Amino -glutaric acid, or glutamic acid. 



D. Hydroxy-mono-amino-di-carboxylic acids. 



Hydroxy-amino-succinic acid. 

 Hydroxy-amino-suberic acid. 



E. Di-amino-mono-carboxylic acids. 



a-/3-diamino-propionic acid, 

 a-e-diamino-caproic acid, or lysine. 

 a-5-diamino- valeric acid, or ornithine. 



F. Subsfrituted-mono-amino-mono-carboxylic acids. 



a-amino-5-guanidine-valeric acid, or arginine. 

 a-amino-/?-iminazolyl propionic acid, or histidine. 

 The constitution of arginine and histidine is as below : 



Arginine. Histidine. 



CH 2 NH CH-N 



| ^C-NH 2 || >CH. 



CH 2 NH C-NH 



CHg v/Hg 



CH :NH 2 CH NH 2 



COOH COOH 



^-phenyl-a-amino-propionic acid, or phenyl-alanine. 

 /9-p-oxy-phenyl-a-amino-propionic acid, or tyrosine. 

 Indole-amino-propionic acid, or tryptophane. 



