THE PROTEINS 41 



CLASSIFICATION OF PROTEINS 



The knowledge of the chemistry of the proteins which is slowly 

 progressing under Emil Fischer's leadership will no doubt in time 

 enable us to give a classification of the substances on a strictly 

 chemical basis. But until that time arrives we must be content very 

 largely with the artificial classification (on the basis of solubility and 

 so forth) which has hitherto prevailed. The following classification 

 must therefore be regarded as a provisional one, which, w T hile it retains 

 the old familiar names as far as possible, yet attempts also to 

 incorporate some of the new ideas. The classes of proteins, then, 

 beginning with the simplest, are as follow : 



1. Protamines. 



2. Histones. 



3. Albumins. 



4. Globulins. 



5. Sclero-proteins. 



6. Phospho-proteins. 



7. Conjugated proteins. 



(a) Gluco-proteins. 



(b) Nucleo-proteins. 



(c) Chromo-proteins. 

 We shall take these classes one by one. 



1. The Protamines 



These substances are obtainable from the heads of the spermatozoa 

 of certain fishes, where they occur in combination with nuclein. 

 Kossel's view that they are the simplest proteins in nature has met 

 with general acceptance, and they give such typical protein reactions 

 as the copper sulphate test (Eose's or Piotrowski's reaction). On 

 hydrolytic decomposition they first yield substances of smaller 

 molecular weight analogous to the peptones which are called protones, 

 and then they split up into amino-acids. The number of resulting 

 amino-acids is small as compared with other proteins ; hence the 

 hypothesis that they are simple proteins is confirmed. Notable 

 among their decomposition products are the diamino-acids or hexone 

 bases, which have the following names and formulae : 



Lysine (C G H 14 N 2 2 ) 



Arginine (C 6 H U N 4 O 2 ) 



Histidine (C 6 H 9 N 3 2 ) 



The protamines differ in their composition according to their source, 

 and yield these products in different proportions. 



