SECT, i] PHYSICO-CHEMICAL SYSTEM 289 



nature of vitellin really became clear. They subjected casein 

 and vitellin to the action of trypsin, and studied the time taken under 

 varying conditions for the phosphorus to be split off into soluble 

 form. Ovovitellin, they found, was much more slowly digested than 

 casein, for after 36 days only half of its phosphorus had been made 

 soluble, whereas after 2 or 3 days a large percentage of the casein 

 phosphorus had gone into solution in inorganic form, and most of 

 the rest was present in water-soluble organic combination, i per 

 cent, soda, however, would bring aU the phosphorus of casein into 

 solution in 24 hours. BayUss & Plimmer concluded that ovovitellin 

 and casein were both phosphoproteins, as distinguished from nucleo- 

 protein, where the phosphorus would be present in the prosthetic 

 group and not in the protein itself Plimmer & Scott later found that 

 ovovitellin behaved in the same way to soda. This reaction served 

 to distinguish between phosphoproteins and nucleoproteins, for all 

 the latter, it was found, were stable to alkali and easily split by 

 acids. From the phosphorus distribution in the unincubated hen's 

 egg, Plimmer & Scott concluded that vitelHn accounted for at 

 least 30 per cent, of the phosphorus, and this led them on to their 

 investigation of the changes which take place in the different 

 phosphorus fractions during the development of the embryo. 



The distribution of phosphorus-containing compounds in egg-yolk, 

 as Plimmer & Scott found, makes a very different picture from that of 

 any other tissue. Their summary is shown in the accompanying table 

 (18). It would be extremely interesting to investigate the phosphorus 

 distribution in the white yolk, which at present is altogether uncharted. 



Table 18. Phosphorus in per cent, of the total phosphorus. 



Steudel, Ellinghaus & Gottschalk have recently found that vitellin 

 behaves towards pepsin exactly like casein. The rate of increase of 

 titratable COOH groups during the digestion far exceeds that of 

 NH2 groups, reaching a maximum about the fourth hour. The 



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