212 PINE-STRUCTURE OF PROTOPLASM II 



the chemical treatment. The protamines seem to be strictly limited to 

 fish sperm. In other nuclei, proteins of less basic character have been 

 found, the so-called histones, which have a higher molecular weight 

 and are therefore less soluble. They contain a great variety of amino 

 acids and form a transition to the typical proteins. Their I.E. P. lies 



/ 



NH 

 \ A/W 



CH-CH, -CHi-CHy -NH-Cf 



CO Arg/nine 



NH 



NH^- CHj- CH^-CH^-CH^-CH 



Lysine \q 



/ 



NH 



CH-CH. 

 rQ Alanine 



\ 



^N NH 



CH \ / 



I L-CHj-CH 



^^LH i-iistidine YO 



y 



NH 



\h-ch,-ch(_'^^^ 



/" , CH, 



QQ Leucine 



Fig. 121. Molecular structure of sturine. 



in the alkaline region, up to a p^ of about 8.5 (Pischinger, 1937). 



The ultraviolet absorption of proteins which results from the 

 presence of cyclic amino acids (tyrosine, tryptophan, histidine) is 

 small. The globulins, for instance, whose I. E. P. lies on the acid side, 

 show a weak absorption band at 2800 A, whereas in the basic histones 

 this band occurs at 2900 A, which may be used as a means of identi- 

 fication (Caspersson, 1 941). The histones appear to be concentrated 

 in the nucleolus. 



The nucleic acids also possess a pronounced chain structure. The 

 chemistry of the chain members, designated as nucleotides, is well- 

 known. Hydrolysis leads to three components: one molecule of 

 phosphoric acid, one molecule of sugar from the group of the pentoses 

 and one heterocyclic basic ring from the pyrimidine or purine type. 

 d-Ribose or desoxyribose is the pentose of the majority of the nucleo- 

 tides isolated, while all kinds of substituted pyrimidine rings (uracil, 



