290 THE PHYSIOLOGY OF REPRODUCTION 



Although differing in many respects from the protein sub- 

 stances, the protamines have been shown by Kossel to have a 

 constitution so similar to that of the proteins that they are now 

 considered to represent one group of the protein substances. 



The study of the products of hydrolytic decomposition shows 

 that while in the case of the typical proteins, such as the proteins 

 of muscle, of milk, or of the serum, the nitrogen is bound up in 

 the form of a great many different substances, e.g. tyrosine, 

 leucine, alanine, glycine, cystine, &c., of which as many as fifteen 

 have been isolated, the protamine molecule is composed of only 

 a few constituent substances. And, further, while in the case of 

 the typical proteins the main bulk of the substance obtained on 

 hydrolysis belongs to the monoamino acids, the protamines are 

 composed largely of the diamino acids : arginine, lysine, and 

 histidine, which, from their basic nature and the fact that they 

 contain six carbon atoms, have received the name " hexone- 

 bases." 



Of these the most important one is arginine, which, on 

 boiling with baryta, is decomposed into urea and diamino- 

 valerianic acid (ornithin), and has the structure 



NH 2 NH 2 



NH = C-NH-CH 2 -CH 2 -CH 2 -CH-COOH 



In salmine, for instance, eight-ninths of the nitrogen is bound 

 up as arginine, while the remainder of the nitrogen is present 

 in the form of monoamino acids, viz., serine, monoamino valerianic 

 acid and proline, in the following proportions : 10 molecules of 

 arginine + 2 molecules of serine + 2 molecules of proline + 1 

 molecule of aminovalerianic acid. Similar relations are found 

 to exist in the case of scombrine and clupeine. In both these 

 protamines eight-ninths of the total nitrogen is present in the 

 form of arginine, which is combined with alanine and proline 

 in the case of scombrine, and with alanine, proline, serine, and 

 aminovalerianic acid in the case of clupeine. 



Since eight-ninths of the nitrogen of these three protamines 

 is present in the form of arginine, and since arginine contains 

 four nitrogen atoms, while the amino acids with which it is 

 combined contain only one nitrogen atom, it follows that in 



