76 THE CHEMICAL CONSTITUENTS OF THE BODY 



Little is known yet with regard to the constitution of paranuclein, or the 

 form in which phosphorus is found either in it or in the nucleo-albumins 

 in general. Levene and Alsberg however have isolated an acid (vitellinic 

 acid) from vitellin which possibly represents a compound of proteid with 

 phosphoric acid in the form of an ester. Like the corresponding pseudo- 

 nuclein this acid contains iron in organic combination, which, as Bunge be- 

 lieves, may serve for the formation of the iron-containing haemoglobin of the 

 young bird. Likewise from casein a paranucleinic acid has been obtained by 

 Salkowski, from which orthophosphoric acid can be split off. 



Neither casein nor vitellin contains any carbohydrate group. Twenty-seven 

 and one-tenth per cent of the total nitrogen in cow's-milk casein occurs as 

 diamino-N, and sixty-two per cent as monamino-N. The maximal yield of 

 tyrosin from casein is 4.5 per cent. Only about one-tenth of the sulphur of 

 casein is present in the form of cystin compounds (Morner). 



C. Nucleins: compounds of proteid with the nucleic acids. 



The nucleic acids are phosphorus-containing substances which yield on 

 decomposition, besides phosphoric or metaphosphoric acid: different charac- 

 teristic purin bases; the pyrimidin derivatives thymin, uracil, and cytosin; 

 and finally carbohydrates. Moreover they are dextro-rotatory, notwithstand- 

 ing that nucleins and even the nucleo-proteids (see below) are laevo-rotatory. 



1. The purin bases (called also alloxuric, xanthin, or nuclein bases) are 

 derivatives of purin, which, according to Fischer, consists of a pyrimidin 

 nucleus and a glyoxalin nucleus joined to the former in the 4, 5 position, 



(1)N CH(6) 



(2)HC (5)0 NH(7) 



II II >CH(8) 

 (3)N 0(4) N(9). 



Different hydrogen atoms of this structure may be replaced by hydroxyl, amid, 

 or alkyl groups. The purin bases are : xanthin (2.6.dioxypurin, C 5 H 4 N 4 O 2 ) ; 

 guanin (2.amino-6.oxypurin, C 5 H 6 N 6 O) ; hypoxanthin (G.oxypurin, CJI 4 N 4 O) ; 

 and adenin (G.amino-purin, C 5 H 5 N 5 ). In guanylic acid from the pancreas only 

 guanin is found. Several purin bases occur in the other nucleic acids and in 

 the nucleic acid from yeast all of them are found. 



2. Thymin, discovered by Kossel in the nucleic acid of the thymus, is 

 5.methyl-2.6.dioxy-pyrimidin, 



NH CO 



00 C-CH 3 



i ii 



NH OH. 



It has been found also in the nucleic acids of the spleen, of fish sperm, of the 

 brain, liver and pancreas. 



3. Uracil, 2.6-dioxy-pyrimidin, 



NH CO 

 OC CH 

 NH-CH 



occurs in the nucleic acid of yeast and in those of the pancreas, thymus, herring 

 sperm, etc. (Ascoli). 



