CHEMICAL COMPOSITION OF PROTEIN MOLECULE 45 



Histones. 



Histonesare distinguished from protaminesin their smaller content of 

 diamino acids, namely, about 30 per cent. Only in the case of thymus- 

 histone has an estimation been made of the monoamino acids. Histones 

 are supposed to be intermediate compounds between protamines and 

 other proteins, and this supposition is confirmed by the results of 

 analysis. 



The protein constituent globin of haemoglobin has always been 

 regarded as a histone, but the presence of only 20 per cent, of diamino 

 acids is against this supposition. Further, the principal diamino acid 

 is histidine, whereas in the other histones it is arginine. It should be 

 noted that haemoglobin contains a considerably greater amount of 

 histidine than the other proteins. The high content in histidine 

 appears to be a peculiarity of the haemoglobins ; it may be connected 

 with the origin of the red blood corpuscles from nucleated corpuscles 

 since the glyoxaline ring contained in histidine is also contained in 

 the purine bases, which are present in nucleic acid. Comparative 

 data of the haemoglobin of different animals by Abderhalden and 

 Medigreceanu are at present only available for the red-blood corpuscles ; 

 those of the horse contain 5-3 per cent, of the hen 2-8 per cent, of 

 the duck 2*5 per cent, of the goose 3*6 per cent. 



Albumins and Globulins. 



Albumins contain no glycine, whereas globulins contain this amino 

 acid ; they show no other striking differences. Their differentiation 

 on physical grounds is thus scarcely borne out by analysis, and their 

 interconversion, which has been described, may be possible. 



The most recent results for crystallised egg-albumin by Osborne, 

 Jones and Leavenworth confirm the earlier ones by Abderhalden and 

 Pregl. They show that workers in different parts obtain very similar 

 results with Fischer's ester method. 



The comparative data by Abderhalden and Slavu, both of serum 

 albumin and serum globulin, with regard to their content in glycine, 

 tyrosine, and glutamic acid would incline one to believe that both the 

 serum albumins and the serum globulins of different origin were of the 

 same composition. 



Chapman and Petrie have determined that egg-white contains 2*4 

 per cent, of arginine, 3*2 per cent of lysine, and 07 per cent of 

 histidine, data which were required for experimental work on nutrition. 



