80 PHYSIOLOGY 



boiling for some hours with water, the higher fractions by boiling with baryta. The 

 acids obtained by the hydrolysis can then be further purified by means of fractional 

 crystallisation. 



THE DISINTEGRATION PRODUCTS OF THE PROTEINS. 



By the methods just described the following substances have been 

 isolated from proteins : 



A. FATTY SERIES 





 (1) Mono-amino-acids (Monobasic) 



GLYCINE or GLYCOCOLL This, the simplest member of the group, is 

 ammo-acetic acid : 



I 

 COOH 



It occurs in considerable quantities among the disintegration products of 

 gelatin and to a slight extent among those derived from certain of the pro- 

 teins. Like the other a-amino-acids, it has a sweetish taste, whence its name 

 was derived (7X1^00- = sweet, tco\\rj = glue). 

 ALANINE is a-amino-propionic acid : 



CH 3 



1 



CH.NH 2 



I 

 COOH 



It is optically active, the alanine derived from proteins being dextro- 

 rotatory. 



Closely allied to alanine is the amino-acid SERINE, which was first 

 obtained by the hydrolysis of silk and has since been found as a constituent 

 of a large number of proteins. Its formula is : 



CH 2 OH 



I 

 CH.NH 2 



I 

 COOH 



i.e. it is amino-oxypropionic acid. Its special interest lies in the fact that 

 it was one of the first of the amino-oxy acids to be isolated, and it is possible 

 in these acids that we must seek the intermediate stages between carbo- 

 hydrates and proteins. 



AMINO-VALERIANIC ACID has the formula 



CH 3 CH 3 



V 



CH 



I 

 CH.NH 2 



COOH 

 It occurs only in small quantities in the protein molecule. 



