108 The Biochemistry of Semen 



chain, the C-terminal position is filled by arginyl-arginine (Dirr and 

 Felix, 1932). Arginine-arginine linkages occur also with great fre- 

 quency in the amino acid chain itself (Felix and Schuberth, 1942). 

 The following peptides have been identified as breakdown products 

 of a partial hydrolysis of clupeine: arginyl-arginine, triarginyl- 

 arginine, alanyl-arginyl-arginine, seryl-arginyl-arginine, and alanyl- 

 alanine; on the basis of the available evidence, Felix, Fischer and 

 Krekels (1952) suggested the following sequence of proline (Prol.), 

 arginine (Arg.) and monoamino acids (M.) in clupeine, 



Prol. (Arg. Arg. Arg. Arg. M. M.)^ Arg. Arg. 



Salmine and clupeine, irrespective of their origin, both contain 

 arginine as the sole basic amino acid; in the corresponding nucleo- 

 protamines the ratio between the arginine residues of the protamines 

 and the phosphoric acid equivalents of nucleic acid is not far from 

 unity, usually about 0-95 (Felix, 1951). In other protamines, on the 

 other hand, e.g. percine and sturine, a certain proportion of the 

 basic units is present in the form of histidine and lysine. 



On close inspection of analytical data relating to the various pro- 

 tamines, there stands out a considerable degree of variability in the 

 amino acid composition, even in closely related species. The situa- 

 tion is even more complicated in sperm nucleoproteins which con- 

 tain histones instead of protamines. The histones such as occur for 

 instance, in the sperm nucleoproteins of sea-urchins {arbacine of 

 Mathews, 1897) and cod-fishes (gadushistone and lotahistone) are 

 characterized by a wider range of amino acids, including tyrosine. 

 It is not improbable that some of the observed variations in the 

 amino acid composition of protamines and histones, represent dis- 

 tinct species characteristics analogous to those which are encoun- 

 tered in other proteins, e.g. in the globins of various haemoglobins. 

 On the other hand, however, the standards for the assessment of 

 chemical purity of nuclear proteins are open to criticism, and it is un- 

 certain whether the examined protamines and histones were always 

 really pure. Quite likely a sperm nucleus may contain in some 

 cases more than one basic protein, that is, a main protamine or 

 histone, together with a smaller amount of a 'subsidiary' product 

 (Stedman and Stedman, 1951). Furthermore, there is also the pos- 

 sibility that some of the reported differences in the composition of 



