76 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Phosphoproteins. 



There is no striking peculiarity noticeable in the analyses of the 

 phosphoproteins. If we disregard the small quantity of glycine found 

 in caseinogen by some workers and in vitellin by Abderhalden and 

 Hunter, who used the commercial product in their investigation, we 

 must note the absence of this amino acid in the phosphoproteins. It 

 is also absent from the albumins. Glycine is apparently, from the 

 results obtained by numerous workers, the only amino acid which can 

 be synthesised by the animal body from other products ; if these phos- 

 phoproteins, especially vitellin, really contain no glycine a further proof 

 is given of its synthesis by animals. Abderhalden and Kempe [ 1 907, 2] 

 in their experiments on the synthesis of amino acids in the chick 

 could not detect any differences in the amounts of glycine, tyrosine 

 and glutamic acid at different periods of development. 



Caseinogen. 



Caseinogen has been hydrolysed more frequently than any other 

 protein and was the protein first analysed by E. Fischer [1901] by the 

 ester method. Fischer did not state the yields of the amino acids, but 

 they were given later by Abderhalden [1905]. No data are given for 

 isoleucine. Some samples of caseinogen seem to contain glycine ; in 

 others this unit is not found. 



The analysis of caseinogen by Osborne and Guest [1911, i] is the 

 most recent, and the data given are the highest which have been ob- 

 served by them and other American workers. On account of the im- 

 portance of this protein in nutrition it is very necessary to have as 

 thorough an analysis as possible. The latest analysis has increased 

 our knowledge of the constituent amino acids by about 1 5 per cent. 

 Some 30 per cent, of the protein still remains unaccounted for. Fore- 

 man's unpublished figures indicate that some of the amino acids are 

 present in larger amounts than other workers have found. 



The caseinogens of cow's, goat's, and human milk appear to have 

 the same composition. 



Vitellin, etc. 



Vitellin, which has been analysed by four sets of investigators, has 

 given very different results. The values of Hugounenq [1906] and of 

 Levene and Alsberg [1906] do not correspond with the values of 

 Abderhalden and Hunter [1906, 2] or of Osborne and Jones [1909, i]. 

 The values by the latter workers are the most recent and are probably 

 the most accurate. 



The phosphoproteins in the eggs of fish (ichthulin) and the frog 

 have been analysed by Hugounenq [1904] and by Galimard [1904]. 



