332 A MANUAL OF PHYSIOLOGY 



CHIEF DECOMPOSITION PRODUCTS OF PROTEINS. 



MONOAMINO-ACIDS AND THEIR COMPOUNDS. 



? COOH. 



Glycin or glycocoll (aminoacetic acid), CH,NH 2 C 

 Alanin (aminopropionic acid), CHjCHNHoCOOH. 

 Serin or oxyalanin (oxyaminopropionic acid), 



CH 2 OH . CHNH, . COOH. 



1 1 < 



Aminovalerianic acid, 



Leucin * (a-aminoisobutylacetic acid) 



^ Q f Aspartic or aminosuccinic acid. 

 Q $ 'o \ Glutamic or glutaminic acid. 



5*8 



S- > fTyrosin* (para-oxyphenylaminopropionic acid), 



g S ' I C 6 H 4 OH . CH 2 . CHNHo . COOH. 



d > | Phenylalanin (phenylaminopropionic acid), 

 Mjjfg I C 6 H 5 CH 2 CHNH 2 COOH. 



2 



J2 & co rProlin (pyrrolidin carboxylic acid). 

 "3-jH > [ Oxyprolin (oxypyrrolidin carboxylic acid). 

 ^'-ij (Tryptophane (indol-amtnopropionic acid). 



DIAMINO-ACIDS AND THEIR COMPOUNDS. 



(Lysin (a-e-diaminocaproic acid), C 6 H 14 N 2 O 2 , or 

 g - . CHNHi(CH,)j CHNH 2 COOH. 



S J Arginin (guanidinaminovalerianic acid), C 6 H ]4 N 4 O 2 , or 



\NHCH 2 (CH 2 ) 2 CHNH 2 COOH. 

 Histidin (j8-imidazol-a -aminopropionic acid), C 6 H 9 N 3 Oo. 



Cystin, C e H ]2 N 2 S 2 O 4 (derived from a complex amino-acid, amino- 

 thiolactic acid, containing the greater part of the sulphur 

 of the protein molecule) . 



Ammonia (representing the so-called 'amide-nitrogen/ and liber- 

 ated from the products of acid hydrolysis of proteins by 

 heating the mixture after addition of alkali). 



After the most prolonged artificial digestion with trypsin, a 

 residue of the protein remains unconverted into these relatively 

 simple substances. But even this small portion of the original 

 protein has undergone a great change, for it no longer gives the 

 biuret reaction. It can be split into amino-acids, etc., by heating 

 with acid. When trypsin acts upon protein already digested 

 by pepsin, this partially hydrolysed residue is smaller than when 

 the trypsin acts alone, no matter for how long a time. This 

 illustrates the co-operative relation of these two ferments a 



* Leucin is formed from a-isobutyl acetic acid by the replacement of 

 one H by NH 2 . Tyrosin is related to propionic acid (C 3 H 6 O 2 ). If one 

 H in propionic acid is replaced by NH 2 , we get aminopropionic acid, 

 C 3 H 5 (NH 2 )O 2 . If another H is replaced by oxyphenyl (C fi H 4 OH), an 

 aromatic radicle, we get tyrosin. 



