CH. XXVIII.] CLASSIFICATION OF PROTEINS 427 



The classes of animal proteins, then, beginning with the simplest, 

 are as follows : 



1. Protamines. 6. Phospho-proteins. 



2. Histones. 7. Conjugated proteins. 



3. Albumins. i. Chromo-proteins. 



4. Globulins. ii. Gluco-proteins. 



5. Sclero-proteins. iii. Nucleo-proteins. 



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 (Kose'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 

 ammo-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, especially arginine. 



The protamines differ in their composition according to their 

 source, and yield these products in different proportions. 



Salmine (from the salmon roe) and clupeine (from the herring roe) appear to be 

 identical, and have the empirical formula C. ?0 H 57 N 17 O 6 ; its principal decomposi- 

 tion product is arginine, but amino- valeric acid and a small quantity of serine and 

 proline are also found. Sturine (from the sturgeon) yields the same products with 

 lysine and histidine in addition. With one exception, the protamines yield no 

 aromatic amino-acids. The exception is cyclopterine (from Cyclopterus lumptus] ; 

 this substance is thus an important chemical link between the other protamines 

 and the more complex members of the protein family. 



2. The Histones. 



These are substances which have been separated from blood- 

 corpuscles ; globin, the protein constituent of haemoglobin, is a well- 

 marked instance. They yield a larger number of amino-compounds 

 than do the protamines, but diamino-acids are relatively abundant. 

 They are coagulable by heat, soluble in dilute acids, and precipitable 

 from such solutions by ammonia. The precipitability by ammonia is 

 a property possessed by no other protein group. 



3. The Albumins. 



These are typical proteins, and yield the majority of the cleavage 

 products already enumerated. 



